Deposição de filmes finos de SnO2 e GaAs, visando confecção de dispositivos baseados na heterojunção SnO2/GaAs

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Color tunability of intense upconversion emission from Er3+-Yb3+ co-doped SiO2-Ta2O5 glass ceramic planar waveguides

This work reports on the infrared-to-visible CW frequency upconversion from planar waveguides based on Er3+-Yb3+-doped 100-xSiO(2)-xTa(2)O(5) obtained by a sol-gel process and deposited onto a SiO2-Si substrate by dip-coating. Surface morphology and optical parameters of the planar waveguides were analyzed by atomic force microscopy and the m-line technique. The influence of the composition on the electronic properties of the glass-ceramic films was followed by the band gap ranging from 4.35 to 4.51 eV upon modification of the Ta2O5 content. Intense green and red emissions were detected from the upconversion process for all the samples after excitation at 980 nm. The relative intensities of the emission bands around 550 nm and 665 nm, assigned to the H-2(11/2) -> I-4(15/2), S-4(3/2) -> I-4(15/2), and F-4(9/2) -> I-4(15/2) transitions, depended on the tantalum oxide content and the power of the laser source at 980 nm. The upconversion dynamics were investigated as a function of the Ta2O5 content and the number of photons involved in each emission process. Based on the upconversion emission spectra and 1931CIE chromaticity diagram, it is shown that color can be tailored by composition and pump power. The glass ceramic films are attractive materials for application in upconversion lasers and near infrared-to-visible upconverters in solar cells.

Utilizzo di dispositivi magnetici nel trattamento della patologia artrosica del ginocchio

The use of scaffolds for Tissue Engineering (TE) is increasing due to their efficacy in helping the body rebuild damaged or diseased tissue. Hydroxyapatite (HA) is the most suitable bioactive ceramic to be used in orthopaedic reconstruction since it replicates the mineral component of the hard tissues, and it has therefore excellent biocompatibility properties. The temporal and spatial control of the tissue regeneration process is the limit to be overcome in order to treat large bone and osteochondral defects. In this thesis we describe the realization of a magnetic scaffolds able to attract and take up growth factors or other bio-agents in vivo via a driving magnetic force. This concept involves the use of magnetic nanoparticles (MNP) functionalized with selected growth factors or stem cells. These functionalized MNP act as shuttles transporting the bio-agents towards and inside the scaffold under the effect of the magnetic field, enhancing the control of tissue regeneration processes. This scaffold can be imagined as a fixed “station” that provides a unique possibility to adjust the scaffold activity to the specific needs of the healing tissue. Synthetic bone graft substitutes, made of collagen or biomineralized collagen (i.e. biomimetic Hydroxyapatite/collagen composites) were used as starting materials for the fabrication of magnetic scaffolds. These materials are routinely used clinically to replace damaged or diseased cartilaginous or bone tissue. Our magnetization technique is based on a dip-coating process consisting in the infilling of biologically inspired porous scaffolds with aqueous biocompatible ferrofluids’ suspensions. In this technique, the specific interconnected porosity of the scaffolds allows the ferrofluids to be drawn inside the structure by capillarity. A subsequent freeze-drying process allows the solvent elimination while keeping very nearly the original shape and porosity of the scaffolds. The remaining magnetic nanoparticles, which are trapped in the structure, lead to the magnetization of the HA/Collagen scaffold. We demonstrate here the possibility to magnetize commercially available scaffolds up to magnetization values that are used in drug delivery processes. The preliminary biocompatibility test showed that the investigated scaffolds provide a suitable micro-environment for cells. The biocompatibility of scaffold facilitates the growth and proliferation of osteogenic cells.

New polymeric materials for vascular surgery

The dramatic impact that vascular diseases have on human life quality and expectancy nowadays is the reason why both medical and scientific communities put great effort in discovering new and effective ways to fight vascular pathologies. Among the many different treatments, endovascular surgery is a minimally-invasive technique that makes use of X-ray fluoroscopy to obtain real-time images of the patient during interventions. In this context radiopaque biomaterials, i.e. materials able to absorb X-ray radiation, play a fundamental role as they are employed both to enhance visibility of devices during interventions and to protect medical staff and patients from X-ray radiations. Organic-inorganic hybrids are materials that combine characteristics of organic polymers with those of inorganic metal oxides. These materials can be synthesized via the sol-gel process and can be easily applied as thin coatings on different kinds of substrates. Good radiopacity of organic-inorganic hybrids has been recently reported suggesting that these materials might find applications in medical fields where X-ray absorption and visibility is required. The present PhD thesis aimed at developing and characterizing new radiopaque organic-inorganic hybrid materials that can find application in the vascular surgery field as coatings for the improvement of medical devices traceability as well as for the production of X-ray shielding objects and garments. Novel organic-inorganic hybrids based on different polyesters (poly-lactic acid and poly-ε-caprolactone) and polycarbonate (poly-trimethylene carbonate) as the polymeric phase and on titanium oxide as the inorganic phase were synthesized. Study of the phase interactions in these materials allowed to demonstrate that Class II hybrids (where covalent bonds exists between the two phases) can be obtained starting from any kind of polyester or polycarbonate, without the need of polymer pre-functionalization, thanks to the occurrence of transesterification reactions operated by inorganic molecules on ester and carbonate moieties. Polyester based hybrids were successfully coated via dip coating on different kinds of textiles. Coated textiles showed improved radiopacity with respect to the plain fabric while remaining soft to the touch. The hybrid was able to coat single fibers of the yarn rather than coating the yarn as a whole. Openings between yarns were maintained and therefore fabric breathability was preserved. Such coatings are promising for the production of light-weight garments for X-ray protection of medical staff during interventional fluoroscopy, which will help preventing pathologies that stem from chronic X-ray exposure. A means to increase the protection capacity of hybrid-coated fabrics was also investigated and implemented in this thesis. By synthesizing the hybrid in the presence of a suspension of radiopaque tantalum nanoparticles, PDMS-titania hybrid materials with tunable radiopacity were developed and were successfully applied as coatings. A solution for enhancing medical device radiopacity was also successfully investigated. High metal radiopacity was associated with good mechanical and protective properties of organic-inorganic hybrids in the form of a double-layer coating. Tantalum was employed as the constituent of the first layer deposited on sample substrates by means of a sputtering technique. The second layer was composed of a hybrid whose constituents are well-known biocompatible organic and inorganic components, such as the two polymers PCL and PDMS, and titanium oxide, respectively. The metallic layer conferred to the substrate good X-ray visibility. A correlation between radiopacity and coating thickness derived during this study allows to tailor radiopacity simply by controlling the metal layer sputtering deposition time. The applied metal deposition technique also permits easy shaping of the radiopaque layer, allowing production of radiopaque markers for medical devices that can be unambiguously identified by surgeons during implantation and in subsequent radiological investigations. Synthesized PCL-titania and PDMS-titania hybrids strongly adhered to substrates and show good biocompatibility as highlighted by cytotoxicity tests. The PDMS-titania hybrid coating was also characterized by high flexibility that allows it to stand large substrate deformations without detaching nor cracking, thus being suitable for application on flexible medical devices.

Inorganic-organic hybrid polymers: Solution-processible coating materials for defined surface functionalization

A new class of inorganic-organic hybrid polymers could successfully been prepared by the combination of different polymerization techniques. The access to a broad range of organic polymers incorporated into the hybrid polymer was realized using two independent approaches.rnIn the first approach a functional poly(silsesquioxane) (PSSQ) network was pre-formed, which was capable to initiate a controlled radical polymerization to graft organic vinyl-type monomers from the PSSQ precursor. As controlled radical polymerization techniques atom transfer radical polymerization (ATRP), as well as reversible addition fragmentation chain transfer (RAFT) polymerization could be used after defined tuning of the PSSQ precursor either toward a PSSQ macro-initiator or to a PSSQ macro-chain-transfer-agent. The polymerization pathway, consisting of polycondensation of trialkoxy-silanes followed by grafting-from polymerization of different monomers, allowed synthesis of various functional hybrid polymers. A controlled synthesis of the PSSQ precursors could successfully be performed using a microreactor setup; the molecular weight could be adjusted easily while the polydispersity index could be decreased well below 2.rnThe second approach aimed to incorporate differently derived organic polymers. As examples, polycarbonate and poly(ethylene glycol) were end-group-modified using trialkoxysilanes. After end-group-functionalization these organic polymers could be incorporated into a PSSQ network.rnThese different hybrid polymers showed extraordinary coating abilities. All polymers could be processed from solution by spin-coating or dip-coating. The high amount of reactive silanol moieties in the PSSQ part could be cross-linked after application by annealing at 130° for 1h. Not only cross-linking of the whole film was achieved, which resulted in mechanical interlocking with the substrate, also chemical bonds to metal or metal oxide surfaces were formed. All coating materials showed high stability and adhesion onto various underlying materials, reaching from metals (like steel or gold) and metal oxides (like glass) to plastics (like polycarbonate or polytetrafluoroethylene).rnAs the material and the synthetic pathway were very tolerant toward different functionalities, various functional monomers could be incorporated in the final coating material. The incorporation of N-isopropylacrylamide yielded in temperature-responsive surface coatings, whereas the incorporation of redox-active monomers allowed the preparation of semi-conductive coatings, capable to produce smooth hole-injection layers on transparent conductive electrodes used in optoelectronic devices.rnThe range of possible applications could be increased tremendously by incorporation of reactive monomers, capable to undergo fast and quantitative conversions by polymer-analogous reactions. For example, grafting active esters from a PSSQ precursor yielded a reactive surface coating after application onto numerous substrates. Just by dipping the coated substrate into a solution of a functionalized amine, the desired function could be immobilized at the interface as well as throughout the whole film. The obtained reactive surface coatings could be used as basis for different functional coatings for various applications. The conversion with specifically tuned amines yielded in surfaces with adjustable wetting behaviors, switchable wetting behaviors or as recognition element for surface-oriented bio-analytical devices. The combination of hybrid materials with orthogonal reactivities allowed for the first time the preparation of multi-reactive surfaces which could be functionalized sequentially with defined fractions of different groups at the interface. rnThe introduced concept to synthesis functional hybrid polymers unifies the main requirements on an ideal coating material. Strong adhesion on a wide range of underlying materials was achieved by secondary condensation of the PSSQ part, whereas the organic part allowed incorporation of various functionalities. Thus, a flexible platform to create functional and reactive surface coatings was achieved, which could be applied to different substrates. rn

Biomimetic coating of organic polymers with a protein-functionalized layer of calcium phosphate: the surface properties of the carrier influence neither the coating characteristics nor the incorporation mechanism or release kinetics of the protein

Polymers that are used in clinical practice as bone-defect-filling materials possess many essential qualities, such as moldability, mechanical strength and biodegradability, but they are neither osteoconductive nor osteoinductive. Osteoconductivity can be conferred by coating the material with a layer of calcium phosphate, which can be rendered osteoinductive by functionalizing it with an osteogenic agent. We wished to ascertain whether the morphological and physicochemical characteristics of unfunctionalized and bovine-serum-albumin (BSA)-functionalized calcium-phosphate coatings were influenced by the surface properties of polymeric carriers. The release kinetics of the protein were also investigated. Two sponge-like materials (Helistat® and Polyactive®) and two fibrous ones (Ethisorb and poly[lactic-co-glycolic acid]) were tested. The coating characteristics were evaluated using state-of-the-art methodologies. The release kinetics of BSA were monitored spectrophotometrically. The characteristics of the amorphous and the crystalline phases of the coatings were not influenced by either the surface chemistry or the surface geometry of the underlying polymer. The mechanism whereby BSA was incorporated into the crystalline layer and the rate of release of the truly incorporated depot were likewise unaffected by the nature of the polymeric carrier. Our biomimetic coating technique could be applied to either spongy or fibrous bone-defect-filling organic polymers, with a view to rendering them osteoconductive and osteoinductive.

Effect of substrate surface roughening and cold spray coating on the fatigue life of AA2024 specimens

The effects of cold spray coating and substrate surface preparation on crack initiation under cyclic loading have been studied on Al2024 alloy specimens. Commercially pure (CP) aluminum feedstock powder has been deposited on Al2024-T351 samples using a cold-spray coating technique known as high velocity particle consolidation. Substrate specimens were prepared by surface grit blasting or shot peening prior to coating. The fatigue behavior of both coated and uncoated specimens was then tested under rotating bend conditions at two stress levels, 180 MPa and 210 MPa. Scanning electron microscopy was used to analyze failure surfaces and identify failure mechanisms. The results indicate that the fatigue strength was significantly improved on average, up to 50% at 180 MPa and up to 38% at 210 MPa, by the deposition of the cold-sprayed CP-Al coatings. Coated specimens first prepared by glass bead grit blasting experienced the largest average increase in fatigue life over bare specimens. The results display a strong dependency of the fatigue strength on the surface preparation and cold spray parameters

Inmovilización de TiO2 sobre polímeros transparentes en el UV-A para la eliminación fotocatalítica de tricloroetileno en aire

El gran desarrollo industrial y demográfico de las últimas décadas ha dado lugar a un consumo crecientemente insostenible de energía y materias primas, que influye negativamente en el ambiente por la gran cantidad de contaminantes generados. Entre las emisiones tienen gran importancia los compuestos orgánicos volátiles (COV), y entre ellos los compuestos halogenados como el tricloroetileno, debido a su elevada toxicidad y resistencia a la degradación. Las tecnologías generalmente empleadas para la degradación de estos compuestos presentan inconvenientes derivados de la generación de productos tóxicos intermedios o su elevado coste. Dentro de los procesos avanzados de oxidación (Advanced Oxidation Processes AOP), la fotocatálisis resulta una técnica atractiva e innovadora de interés creciente en su aplicación para la eliminación de multitud de compuestos orgánicos e inorgánicos, y se ha revelado como una tecnología efectiva en la eliminación de compuestos orgánicos volátiles clorados como el tricloroetileno. Además, al poder aprovechar la luz solar como fuente de radiación UV permite una reducción significativa de costes energéticos y de operación. Los semiconductores más adecuados para su empleo como fotocatalizadores con aprovechamiento de la luz solar son aquellos que tienen una banda de energía comparable a la de los fotones de luz visible o, en su defecto, de luz ultravioleta A (Eg < 3,5 eV), siendo el más empleado el dióxido de titanio (TiO2). El objetivo principal de este trabajo es el estudio de polímeros orgánicos comerciales como soporte para el TiO2 en fotocatálisis heterogénea y su ensayo para la eliminación de tricloroetileno en aire. Para ello, se han evaluado sus propiedades ópticas y su resistencia a la fotodegradación, y se ha optimizado la fijación del fotocatalizador para conseguir un recubrimiento homogéneo, duradero y con elevada actividad fotocatalítica en diversas condiciones de operación. Los materiales plásticos ensayados fueron el polietileno (PE), copolímero de etil vinil acetato con distintos aditivos (EVA, EVA-H y EVA-SH), polipropileno (PP), polimetil (metacrilato) fabricado en colada y extrusión (PMMA-C y PMMA-E), policarbonato compacto y celular (PC-C y PC-Ce), polivinilo rígido y flexible (PVC-R y PVC-F), poliestireno (PS) y poliésteres (PET y PETG). En base a sus propiedades ópticas se seleccionaron el PP, PS, PMMA-C, EVA-SH y PVC-R, los cuales mostraron un valor de transmitancia superior al 80% en el entorno de la región estudiada (λ=365nm). Para la síntesis del fotocatalizador se empleó la tecnología sol-gel y la impregnación multicapa de los polímeros seleccionados por el método de dip-coating con secado intermedio a temperaturas moderadas. Con el fin de evaluar el envejecimiento de los polímeros bajo la radiación UV, y el efecto sobre éste del recubrimiento fotoactivo, se realizó un estudio en una cámara de exposición a la luz solar durante 150 días, evaluándose la resistencia química y la resistencia mecánica. Los resultados de espectroscopía infrarroja y del test de tracción tras el envejecimiento revelaron una mayor resistencia del PMMA y una degradación mayor en el PS, PVC-R y EVA SH, con una apreciable pérdida del recubrimiento en todos los polímeros. Los fotocatalizadores preparados sobre soportes sin tratamiento y con tres capas de óxido de titanio mostraron mejores resultados de actividad con PMMA-C, PET y PS, con buenos resultados de mineralización. Para conseguir una mayor y mejor fijación de la película al soporte se realizaron tratamientos químicos abrasivos con H2SO4 y NaOH y tratamientos de funcionalización superficial por tecnología de plasma a presión atmosférica (APP) y a baja presión (LPP). Con los tratamientos de plasma se consiguió una excelente mojabilidad de los soportes, que dio lugar a una distribución uniforme y más abundante del fotocatalizador, mientras que con los tratamientos químicos no se obtuvo una mejora significativa. Asimismo, se prepararon fotocatalizadores con una capa previa de dióxido de silicio con la intervención de surfactantes (PDDA-SiO2-3TiO2 y SiO2FC-3TiO2), consiguiéndose buenas propiedades de la película en todos los casos. Los mejores resultados de actividad con tratamiento LPP y tres capas de TiO2 se lograron con PMMA-C (91% de conversión a 30 ppm de TCE y caudal 200 ml·min-1) mejorando significativamente también la actividad fotocatalítica en PVC-R y PS. Sin embargo, el material más activo de todos los ensayados fue el PMMA-C con el recubrimiento SiO2FC-3TiO2, logrando el mejor grado de mineralización, del 45%, y una velocidad de 1,89 x 10-6 mol· m-2 · s-1, que dio lugar a la eliminación del 100 % del tricloroetileno en las condiciones anteriormente descritas. A modo comparativo se realizaron ensayos de actividad con otro contaminante orgánico tipo, el formaldehído, cuya degradación fotocatalítica fue también excelente (100% de conversión y 80% de mineralización con 24 ppm de HCHO en un caudal de aire seco de 200 ml·min-1). Los buenos resultados de actividad obtenidos confirman las enormes posibilidades que ofrecen los polímeros transparentes en el UV-A como soportes del dióxido de titanio para la eliminación fotocatalítica de contaminantes en aire. ABSTRACT The great industrial and demographic development of recent decades has led to an unsustainable increase of energy and raw materials consumption that negatively affects the environment due to the large amount of waste and pollutants generated. Between emissions generated organic compounds (VOCs), specially the halogenated ones such as trichloroethylene, are particularly important due to its high toxicity and resistance to degradation. The technologies generally used for the degradation of these compounds have serious inconveniences due to the generation of toxic intermediates turn creating the problem of disposal besides the high cost. Among the advanced oxidation processes (AOP), photocatalysis is an attractive and innovative technique with growing interest in its application for the removal of many organic and inorganic compounds, and has emerged as an effective technology in eliminating chlorinated organic compounds such as trichloroethylene. In addition, as it allows the use of sunlight as a source of UV radiation there is a significant reduction of energy costs and operation. Semiconductors suitable to be used as photocatalyst activated by sunlight are those having an energy band comparable to that of the visible or UV-A light (Eg <3,5 eV), being titanium dioxide (TiO2), the most widely used. The main objective of this study is the test of commercial organic polymers as supports for TiO2 to be applied in heterogeneous photocatalysis and its assay for removing trichloroethylene in air. To accomplish that, its optical properties and resistance to photooxidation have been evaluated, and different operating conditions have been tested in order to optimize the fixation of the photocatalyst to obtain a homogeneous coating, with durable and high photocatalytic activity. The plastic materials tested were: polyethylene (PE), ethyl vinyl acetace copolymers with different additives (EVA, EVA-H and EVA -SH), polypropylene (PP), poly methyl (methacrylate) manufactured by sheet moulding and extrusion (PMMA-C and PMMA-E), compact and cellular polycarbonates (PC-C PC-Ce), rigid and flexible polyvinyl chloride (PVC-R and PVC-F), polystyrene (PS) and polyesters (PET and PETG). On the basis of their optical properties PP, PS, PMMA-C, EVA-SH and PVC-R were selected, as they showed a transmittance value greater than 80% in the range of the studied region (λ = 365nm). For the synthesis of the photocatalyst sol-gel technology was employed with multilayers impregnation of the polymers selected by dip-coating, with intermediate TiO2 drying at moderate temperatures. To evaluate the polymers aging due to UV radiation, and the effect of photoactive coating thereon, a study in an sunlight exposure chamber for 150 days was performed, evaluating the chemical resistance and the mechanical strength. The results of infrared spectroscopy and tensile stress test after aging showed the PMMA is the most resistant sample, but a greater degradation in PS, PVC-R and EVA SH, with a visible loss of the coating in all the polymers tested. The photocatalysts prepared on the untreated substrates with three layers of TiO2 showed better activity results when PMMA-C, PET and PS where used. To achieve greater and better fixation of the film to the support, chemical abrasive treatments, with H2SO4 and NaOH, as well as surface functionalization treatments with atmospheric pressure plasma (APP) and low pressure plasma (LPP) technologies were performed. The plasma treatment showed the best results, with an excellent wettability of the substrates that lead to a better and uniform distribution of the photocatalyst compared to the chemical treatments tested, in which no significant improvement was obtained. Also photocatalysts were prepared with the a silicon dioxide previous layer with the help of surfactants (SiO2- 3TiO2 PDDA-and-3TiO2 SiO2FC), obtaining good properties of the film in all cases. The best activity results for LPP-treated samples with three layers of TiO2 were achieved with PMMA-C (91% conversion, in conditions of 30 ppm of TCE and 200 ml·min-1 air flow rate), with a significant improvement of the photocatalytic activity in PVC-R and PS samples too. However, among all the materials assayed, PMMA-C with SiO2FC-3TiO2 coating was the most active one, achieving the highest mineralization grade (45%) and a reaction rate of 1,89 x 10-6 mol· m-2 · s-1, with total trichloroethylene elimination in the same conditions. As a comparative assay, an activity test was also performed with another typical organic contaminant, formaldehyde, also with good results (100% conversion with 24 ppm of HCHO and 200 ml·min-1 gas flow rate). The good activity results obtained in this study confirm the great potential of organic polymers which are transparent in the UV-A as supports for titanium dioxide for photocatalytic removal of air organic pollutants.

Bioinspired Anti-fouling Coating on Hydrophobic Surfaces

Thesis (Master's)--University of Washington, 2016-06

Silica membrane reactors for hydrogen production from water gas shift

This paper presents an analysis of membrane reactor (MR) operation and design for enhanced hydrogen production from the water gas shift (WGS) reaction. It has been established that membrane reactors can enhance an equilibrium limited reaction through product separation. However, the detailed effects of reactor setup, membrane configuration and catalyst volume have yet to be properly analysed for this reaction. This paper investigates new ideas for membrane reactors such as the development of new catalytic films, for improved interaction between the reaction and separation zones. Current membrane reactors utilise a packed bed of catalyst within the membrane tube, utilising a large volume of catalyst to drive reaction. This is still inefficient and provides only limited benefits over conventional WGS reactors. New reactor configurations look to optimise the interactive effects between reaction and separation to provide improved operation. In this paper, thin film catalysts were produced using dip coating and spray coating techniques. This technique produced catalyst coatings with good thickness, though the abrasion strength of the dip coated catalyst was quite low. The catalyst was tested in a packed bed reactor for temperature activity at low temperatures and catalyst activity at varying levels of excess water

Eficiência do processo de recobrimento de sementes de brócolos recobertas com polímero em leito de jorro

Broccoli seeds were coated in a conical-cylindrical spouted bed with an aqueous suspension of hydroxy ethyl cellulose aiming to improve the seeds coating technique using a fluid-dynamic process. An experimental design was applied to investigate the effects of the operating variables: gas temperature, atomizing air pressure and suspension flow rate on the germination of the seeds and on the process efficiency. Results indicated that the operating variables affect both the coating process efficiency and the germination ability. However, the analysis didn t identify differences between the germination potential of coated and uncoated seeds. Coated seeds absorbed up to 10 percent less moisture than the uncoated ones, when the environment temperature and humidity were controlled over a period of time.

High selectivity microporous silica membranes for lactic acid dehydration

Lactic acid (LA) has significant market potential for many industries including food, cosmetics, pharmaceuticals, medical and biodegradable materials. Production of LA usually begins with the fermentation of glucose but subsequent stages for the enrichment of lactic acid are complex and energy intensive and could be minimised using water selective membrane technology. In this work, we trialled a highly selective hydrostable carbonised template molecular sieve silica (CTMSS) membrane for the dehydration of a 15 vol% aqueous lactic acid solution with 0.1 vol% glucose. CTMSS membrane films were developed by dip-coating ceramic substrates with silica sols made using the acid catalysed sol-gel process. Permeation was performed by feeding LA/glucose solution to the membrane cell at 18°C in a standard pervaporation setup. The membrane showed selective transport of water from the aqueous feed to the permeate while glucose was not detected. CTMSS membrane permeate flux stabilised at 0.2 kg.m-2.hr-1 in 3.9 hours, and reduced LA to lower than 0.2 vol%. Flux through the CTMSS micropores was activated, displaying increased initial flux to 1.58 kg.m-2.hr-1 at 60°C. To enrich a 1 l.min-1 stream to 85% LA in a single stage, a minimum membrane area of 324 m2 would be required at 18°C. Increased operating temperature to 80°C significantly reduced this area to 24 m2 but LA levels in the permeate stream increased to 0.5 vol%. The highly selective CTMSS membrane technology is an ideal candidate for LA purification. CTMSS membrane systems operate stably in aqueous systems leading to potential cost reductions in LA processing for future markets.

A new chemical route to synthesise TM-doped (TM = Co, Fe) TiO2 nanoparticles

Since the discovery of ferromagnetism well above room temperature in the Co-doped TiO2 system, diluted magnetic semiconductors based on TiO2 doped with transition metals have generated great interest because of their potential use in the development of spintronic devices. The purpose of this paper is to report on a new and swift chemical route to synthesise highly stable anatase single-phase Co- and Fe-doped TiO2 nanoparticles, with dopant concentrations of up to 10 at.-% and grain sizes that range between 20 and 30 nm. Complementary structural, microstructural and chemical analyses of the different nanopowders synthesised strongly support the hypothesis that a homogeneous distribution of the dopant element in the substitutional sites of the anatase structure has been achieved. Moreover, UV/Vis diffuse reflectance spectra of powder samples show redshifts to lower energies and decreasing bandgap energies with increasing Co or Fe concentration, which is consistent with n-type doping of the TiO2 anatase matrix. Films of Co-doped TiO2 were successfully deposited onto Si (100) substrates by the dip-coating method, with suspensions of Ti1-xCOxO2 nanoparticles in ethylene glycol. ((C)Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

Estudo de técnicas de deposição de filmes finos poliméricos à base de silanos

Dissertação para obtenção do Grau de Mestre em Engenharia de Materiais

Microcystin-LR detection in water by the Fabry–Pérot interferometer using an optical fibre coated with a sol–gel imprinted sensing membrane

Cyanobacteria deteriorate the water quality and are responsible for emerging outbreaks and epidemics causing harmful diseases in Humans and animals because of their toxins. Microcystin-LR (MCT) is one of the most relevant cyanotoxin, being the most widely studied hepatotoxin. For safety purposes, the World Health Organization recommends a maximum value of 1 μg L−1 of MCT in drinking water. Therefore, there is a great demand for remote and real-time sensing techniques to detect and quantify MCT. In this work a Fabry–Pérot sensing probe based on an optical fibre tip coated with a MCT selective thin film is presented. The membranes were developed by imprinting MCT in a sol–gel matrix that was applied over the tip of the fibre by dip coating. The imprinting effect was obtained by curing the sol–gel membrane, prepared with (3-aminopropyl) trimethoxysilane (APTMS), diphenyl-dimethoxysilane (DPDMS), tetraethoxysilane (TEOS), in the presence of MCT. The imprinting effect was tested by preparing a similar membrane without template. In general, the fibre Fabry–Pérot with a Molecular Imprinted Polymer (MIP) sensor showed low thermal effect, thus avoiding the need of temperature control in field applications. It presented a linear response to MCT concentration within 0.3–1.4 μg L−1 with a sensitivity of −12.4 ± 0.7 nm L μg−1. The corresponding Non-Imprinted Polymer (NIP) displayed linear behaviour for the same MCT concentration range, but with much less sensitivity, of −5.9 ± 0.2 nm L μg−1. The method shows excellent selectivity for MCT against other species co-existing with the analyte in environmental waters. It was successfully applied to the determination of MCT in contaminated samples. The main advantages of the proposed optical sensor include high sensitivity and specificity, low-cost, robustness, easy preparation and preservation.