The preparation and properties of coprecipitated Cu-Zr-Y and Cu-Zr-La catalysts used for the steam reforming of methanol

A series of Cu-zirconia catalysts containing various additives (Y2O3, La2O3, Al2O3 and CeO2) have been prepared by coprecipitation and their activities and stabilities under operating conditions have been obtained for the steam reforming of methanol. It has been found that an yttria-promoted catalyst containing 30 mol% Cu and 20 mol% of Y2O3 is not only very active but is also very stable under reaction conditions. The yttria appears to stabilise a high copper surface area and may also have a slight promotional effect on the copper. The results obtained with this material compare very favourably with data for the best catalysts reported in the literature. (C) 2007 Published by Elsevier B.V.

Listening to lanthanide complexes: Determination of the intrinsic luminescence quantum yield by nonradiative relaxation

The photophysical properties of lanthanide complexes have been studied extensively; however, fundamental parameters such as the intrinsic quantum yield as well as radiative and nonradiative decay rates are difficult or even impossible to measure experimentally. Herein, a photoacoustic (PA) method is proposed to determine the intrinsic quantum yield of lanthanide complexes with lifetimes in the order of milliseconds. This method is used to determine the intrinsic quantum yields for europium (III)-containing metallomesogens as well as terbium(III) complexes. The results show that the PA signal is sensitive to both the lifetime and the ratio of the fast-to-slow heat component of the samples. It is found that there is an efficient ligand sensitization and a moderate intrinsic quantum yield for the complexes. The intrinsic quantum yield of Eu3+ in the metallomesogens exhibits an obvious increase upon the isotropic liquid to smectic A transition. The proposed PA method is quite simple, and con contribute to a clearer understanding of the photophysical processes in luminescent lanthanide complexes.

Luminescence of LaF3:Ln(3+) Nanocrystal Dispersions in Ionic Liquids

Ionic liquids were used as solvents for dispersing luminescent lanthanide-doped LaF3:Ln(3+) nanocrystals (Ln(3+) = Eu3+ and Nd3+). To increase the solubility of the inorganic nanoparticles in the ionic liquids, the nanocrystals were prepared with different stabilizing ligands, i.e., citrate, N,N,N-trimethylglycine (betaine), and lauryldimethylglycine (lauryl betaine). LaF3:5%Ln(3+) :betaine could successfully be dispersed in 1-butyl-1-methylpyrrolidinium bis(tiifluoromethylsulfonyl)imide [C(4)mpyr][Tf2N], 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate [C(4)mpyr][TfO], and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C(4)mim][Tf2N] but only in limited amounts. Red photoluminescence was observed for the europium(III)-containing nanoparticles and near-infrared luminescence for the neodymium(III)-containing systems.

Effect of titania addition on yttria-stabilised tetragonal zirconia ceramics sintered at high temperatures

<p>In order to combine the mechanical properties of yttria-stabilised zirconia (ZrO2-3 mol% Y2O3; code Y-ZrO2) with the bioactivity of titania (TiO2), Y-ZrO2-TiO2, green compacts with 0-40vol.% TiO2 were sintered at 1300, 1400, and 1500degreesC for 4h, respectively. The microstructural features such as grains, pores, and phases were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDX). The mechanical properties such as hardness and toughness were also determined using the methods of Vickers indentation and Knoop indentation. All the composites showed the major tetragonal Y-ZrO2 phase regardless of the content of the added TiO2. However, rutile TiO2 phase was obtained at 1300degreesC, whereas zirconium titanate (ZrTi04) phase was found at 1400 and 1500degreesC. The Y-ZrO2-ZrTiO4 Composites sintered at 1500degreesC showed relatively high hardness (860-1000 kg/mm(2)) and toughness (4.0-4.5 MPa m(0.5)), whereas the Y-ZrO2-TiO2 composites sintered at 1300degreesC had slightly lower hardness (720-950kg/mm(2)) and fracture toughness (3.1-3.3 MPa m(0.5)). (C) 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved.</p>

Development of sialons colloidally processed in aqueous medium

Desenvolveu-se um novo m��todo de processamento coloidal em meio aquoso para consolidar cer��micos de ��-Y-SiAlON, os quais foram sinterizados por prensagem isost��tica a quente (HIP) e por spark plasma sintering (SPS). Preparou-se com sucesso uma suspens��o aquosa de p��s precursores de YSiAlON (Si3N4, Al2O3, Y2O3 e AlN), temporariamente est��vel, usando Dolapix PC21 como dispersante, permitindo a fabrica����o de p��s granulados pela t��cnica de aspers��o-congelamento-liofiliza����o e a consolida����o de corpos em verde por enchimento por barbotina. Avaliou-se o efeito do excesso de oxig��nio introduzido pelo processamento aquoso no desenvolvimento microestrutural e nas propriedades mec��nicas. Os corpos de Y-SiAlON consolidados por enchimento por barbotina e sinterizados por HIP a 1800��C apresentaram microestruturas e propriedades mec��nicas similares a corpos consolidados por prensagem a seco. Estes materiais exibiram densifica����o completa, dureza Vickers m��xima de 2003 e tenacidade �� fractura (m��todo SEVNB) m��xima de 5.20 MPam1/2. Foi ainda poss��vel estabelecer uma rela����o estreita entre o aumento do conte��do em oxig��nio das amostras sinterizadas e a diminui����o da tenacidade �� fractura. Na tentativa de melhorar a tenacidade �� fractura dos materiais, procedeu-se �� incorpora����o nas suspens��es de sementes de Ca-��-SiAlON de geometria alongada produzidas por s��ntese por combust��o, adicionadas como agentes de refor��o. A s��ntese por combust��o realizada em larga escala (cargas at�� 1 kg) n��o produziu efeitos negativos ��bvios nos produtos da reac����o. Investigara-se os efeitos da adi����o de 5 % em peso de sementes nas propriedades mec��nicas e no desenvolvimento microestrutural de amostras densificadas por HIP. Em compara����o com os materiais sem sementes, a tenacidade �� fractura (m��todo SEVNB) aumentou 13%, mas a dureza Vickers resultou 14,5% inferior. A sinteriza����o por SPS permitiu obter densifica����o completa a temperaturas t��o baixas como 1600��C a partir dos p��s granulados de Y-SiAlON sem a adi����o extra de Y2O3 para aumentar o teor de fase l��quida. Os materiais sinterizados a 1700��C e 1600��C mostraram valores m��ximos de tenacidade �� fractura de 4.36 e 4.20 MPam1/2 (m��todo SEVNB), e de dureza Vickers de 2089 e 2084, respectivamente. Esta t��cnica de sinteriza����o permitiu ainda obter corpos sinterizados transl��cidos com uma transmit��ncia m��xima de 61% numa amostra de 2mm de espessura. Os corpos transl��cidos apresentaram dureza Vickers de 2154 e tenacidade �� fractura 3.74 MPam1/2 (m��todo SEVNB).

Lanthanide oxide nanotubes and nanorods: synthesis, processing, luminescence and catalytic properties

Esta tese relata estudos de s��ntese, caracteriza����o da estrutura e das propriedades de fotoluminesc��ncia e aplica����es de nanotubos e nanobastonetes de ��xidos de lantan��deos em pontas para microscopia de for��a at��mica, cat��lise heterog��nea e comp��sitos de base polim��rica. H�� um interesse crescente em compreender como o confinamento qu��ntico decorrente da redu����o do tamanho de part��cula pode influenciar a efici��ncia da luminesc��ncia, a din��mica dos estados excitados, a transfer��ncia de energia e os efeitos de termaliza����o de nanolumin��foros. Em nanocristais dopados com lantan��deos (Ln3+), e apesar da localiza����o dos estados 4f, ocorrem efeitos de confinamento qu��ntico via interac����o com os modos vibracionais da rede. Em particular, a termaliza����o an��mala, descrita para uma variedade de nanocristais dopados com Ln3+, tem sido atribu��da �� aus��ncia de modos vibracionais de menor frequ��ncia. Este nanoconfinamento pode ter impacto na din��mica da luminesc��ncia, bem como na transfer��ncia de energia mediada por modos vibracionais e processos de upconversion. Nesta tese, relata-se o estudo deste efeito em nanotubos de Gd2O3:Eu3+. A influ��ncia de par��metros como a concentra����o de eur��pio e as condi����es de calcina����o tamb��m foi investigada. Algumas aplica����es destes ��xidos de lantan��deos tamb��m foram exploradas, nomeadamente a modifica����o de pontas usadas em microscopia de for��a at��mica com nanobastonetes de Gd2O3:Eu3+, lograda atrav��s de dielectroforese, t��cnica que n��o degrada a emiss��o de luz (rendimento qu��ntico 0.47). As pontas modificadas s��o est��veis sob condi����es de trabalho, podendo ser aplicadas, por exemplo, em microscopia ��ptica de varrimento de campo pr��ximo (SNOM). A oxida����o em fase l��quida do etilbenzendo foi investigada usando como catalisador nanotubos de CeO2, em presen��a dos oxidantes hidroper��xido de t-butilo e H2O2, e do solvente acetonitrilo, e temperaturas entre 55 e 105 ��C. Nanobastonetes de Gd2O3:Eu3+ recobertos com s��lica foram preparados pelo m��todo sol-gel. Esta cobertura resultou num aumento, quer do rendimento qu��ntico de emiss��o, de 0.51 para 0.86 (excita����o a 255 nm), quer dos tempos de vida,de 1.43 para 1.80 ms (excita����o a 394.4 nm). A superf��cie dos nanotubos cobertos com s��lica foi modificada com o agente de acoplamento metacrilato de 3-(trimetoxissilil)propilo que permitiu a prepara����o de comp��sitos atrav��s da subsequente polimeriza����o in-situ do estireno por t��cnicas de miniemuls��o e solu����o. ABSTRACT: This thesis reports on the synthesis, characterisation of the structure and photoluminescence properties, and applications of nanotubes and nanorods of lanthanides oxides in atomic force microscopy tips, heterogeneous catalysis and polymer-base composites. There is a growing interest in understanding how size-dependent quantum confinement affects the photoluminescence efficiency, excited-state dynamics, energy-transfer and thermalisation phenomena in nanophosphors. For lanthanide (Ln3+)-doped nanocrystals, and despite the localisation of the 4f states, confinement effects are induced mostly via electron-phonon interactions. In particular, the anomalous thermalisation reported for a handful of Ln3+-doped nanocrystals has been rationalised by the absence of lowfrequency phonon modes. This nanoconfinement may further impact on the Ln3+ luminescence dynamics, such as phonon-assisted energy transfer or upconversion processes. Here, this effect is investigated in Gd2O3:Eu3+ nanotubes. The influence of parameters such as europium concentration and calcination procedure is also studied. Some applications of these lanthanides oxides have been explored, for instance the modification of atomic force microscopy tips with photoluminescent Gd2O3:Eu3+ nanorods, using dielectrophoresis, a technique which preserves the red emission of the nanorods (quantum yield 0.47). The modified tips are stable under working conditions and may find applications in scanning near-field optical microscopy. The liquid-phase oxidation of ethylbenzene over CeO2 nanotubes has been investigated, using tert-butyl-hydroperoxide and H2O2 as the oxidising agents, and acetonitrile as the solvent, in the range 55-105 ��C. Gd2O3:Eu3+ nanorods have been coated with silica via a sol-gel approach. The silica coating increases both, the Eu3+ absolute emission quantum yields from 0.51 to 0.86 (255 nm excitation), and decay times from 1.43 to 1.80 ms (394.4 nm excitation). The silica coating was modified with 3- (trimethoxysilyl) propyl methacrylate and, subsequently, composites have been prepared by in-situ radical polymerisation of styrene via miniemulsion and solution routes.

Polioxometalatos: dos agregados moleculares a redes e materiais

Esta disserta����o teve como objectivo principal a prepara����o de novos materiais luminescentes contendo lantanopolioxometalatos. Foram utilizados polioxometalatos (POMs) do tipo Keggin, Wells-Dawson e [Ln(M5O18)2]9- com M (VI) = W, Mo contendo diferentes i��es lantan��deo. Foram sintetizados materiais h��bridos org��nico-inorg��nicos com base em lantanopolioxometalatos e ligandos org��nicos. O efeito da coordena����o destes ligandos org��nicos na luminesc��ncia dos i��es lantan��deo (efeito de antena) foi investigado para os ��cidos picol��nico e 3-hidroxipicol��nico. Os estudos de fotoluminesc��ncia destes materiais permitiram mostrar a exist��ncia de um processo de sensitiza����o da emiss��o dos i��es lantan��deo atrav��s de fen��menos de transfer��ncia de energia dos ligandos e do POM para o centro emissor. No caso particular dos materiais h��bridos contendo POMs do tipo Wells-Dawson, a introdu����o do ligando org��nico levou �� intensifica����o da absor����o de energia atrav��s do POM, a qual era praticamente inexistente nos correspondentes lantanopolioxometalatos. Prepararam-se nanocomp��sitos do tipo ���core/shell��� contendo POMs e h��bridos org��nico-inorg��nicos como n��cleo rodeados por uma camada de s��lica. Os nanocomp��sitos preparados apresentam uma estrutura ���core/shell��� bem definida com um di��metro m��dio de aproximadamente 35 nm. As t��cnicas de microscopia electr��nica, nomeadamente o mapeamento por EDX, permitiram confirmar a presen��a dos POMs no n��cleo das nanopart��culas de s��lica. A biofuncionaliza����o destes nanocomp��sitos com um anticorpo foi estudada, com vista �� potencial aplica����o destes sistemas como biomarcadores ��pticos. Os estudos de microscopia de fluoresc��ncia permitiram observar a emiss��o do Eu3+ presente nas nanopart��culas biofuncionalizadas com o anticorpo, utilizando excita����o na zona do ultravioleta. Estes resultados refor��am a viabilidade da aplica����o destes sistemas como marcadores celulares em alternativa a ���quantum dots��� e corantes org��nicos. No ��mbito dos nanomateriais, foi tamb��m preparado um material constitu��do por part��culas de Na9[Eu(W5O18)2] de dimens��es nanom��tricas, utilizando micelas invertidas como nanoreactores, de forma a limitar o tamanho das part��culas. Foi realizada a prepara����o de novos materiais lamelares luminescentes por intercala����o de POMs e respectivos materiais h��bridos em argilas ani��nicas de zinco e alum��nio. A intercala����o foi realizada atrav��s de um m��todo de troca ani��nica directa usando uma argila contendo nitrato como ani��o precursor. O estudo por difrac����o de raios-X revelou-se uma t��cnica fundamental na caracteriza����o destes materiais, nomeadamente atrav��s da determina����o da altura de galeria. A partir deste par��metro foi poss��vel verificar a orienta����o da esp��cie intercalada na argila. No caso da intercala����o do ani��o do tipo Keggin, o estudo por RMN de 31P MAS permitiu identificar a esp��cie intercalada na argila. As propriedades de luminesc��ncia foram estudadas para a generalidade dos novos materiais preparados.

Multifunctional nanoparticles for MR and fluorescence imaging

In the past few years a new generation of multifunctional nanoparticles (NPs) has been proposed for biomedical applications, whose structure is more complex than the structure of their predecessor monofunctional counterparts. The development of these novel NPs aims at enabling or improving the performance in imaging, diagnosis and therapeutic applications. The structure of such NPs comprises several components exhibiting various functionalities that enable the nanoparticles to perform multiple tasks simultaneously, such as active targeting of certain cells or compartmentalization, imaging and delivery of active drugs. This thesis presents two types of bimodal bio-imaging probes and describes their physical and chemical properties, namely their texture, structure, and 1H dynamics and relaxometry, in order to evaluate their potential as MRI contrast agents. The photoluminescence properties of these probes are studied, aiming at assessing their interest as optical contrast agents. These materials combine the properties of the trivalent lanthanide (Ln3+) complexes and nanoparticles, offering an excellent solution for bimodal imaging. The designed T1- type contrast agent are SiO2@APS/DTPA:Gd:Ln or SiO2@APS/PMN:Gd:Ln (Ln= Eu or Tb) systems, bearing the active magnetic center (Gd3+) and the optically-active ions (Eu3+ and Tb3+) on the surface of silica NPs. Concerning the relaxometry properties, moderate r1 increases and significant r2 increases are observed in the NPs presence, especially at high magnetic fields, due to susceptibility effects on r2. The Eu3+ ions reside in a single low-symmetry site, and the photoluminescence emission is not influenced by the simultaneous presence of Gd3+ and Eu3+. The presence of Tb3+, rather than Eu3+ ion, further increases r1 but decreases r2. The uptake of these NPs by living cells is fast and results in an intensity increase in the T1-weighted MRI images. The optical features of the NPs in cellular pellets are also studied and confirm the potential of these new nanoprobes as bimodal imaging agents. This thesis further reports on a T2 contrast agent consisting of core-shell NPs with a silica shell surrounding an iron oxide core. The thickness of this silica shell has a significant impact on the r2 and r2* relaxivities, and a tentative model is proposed to explain this finding. The cell viability and the mitochondrial dehydrogenase expression given by the microglial cells are also evaluated.

Self-referencing thermometry in the nanoscale

Na ��ultima d��ecada emergiu uma linha de investiga��c��ao muito activa em term��ometros n��ao invasivos e precisos que possam determinar temperatura `a escala nanom��etrica. Esta investiga��c��ao foi fortemente estimulada pelas numerosas solicita��c��oes da nanotecnologia e da biomedicina, por exemplo. Uma das abordagens mais promissoras prop��oe o uso de i��oes trivalentes de lantan����deos que apresenta propriedades fotoluminescentes que dependem da temperatura. Neste trabalho demonstra-se que esta t��ecnica combina as vantagens de te um limite de detec��c��ao de 0.5 graus com sensibilidade at��e 4.5 % �� K���1. Este term��ometro molecular pode ser processado em filmes finos ou nanopart����culas, abrindo os campos de aplica��c��ao a diferentes utiliza��c��oes. As nanopart����culas de s����lica produzidas s��ao caracterizadas na presen��ca e na aus��encia de i��oes lantan����deos. Sem o metal, as nanopart����culas de APTES/TEOS demonstram ser luminescentes sob excita��c��ao UV sem necessidade de utilizar qualquer tratamento t��ermico. O rendimento qu��antico de emiss��ao depende apenas da propor��c��ao dos silanos e pode atingir o valor de 0.15 �� 0.02. A co-dopagem destas nanopart����culas com Eu3+ e Tb3+ permite obter sondas com resposta raciom��etrica, com a possibilidade de ajustar a gama de temperaturas de opera��c��ao e a sensibilidade, via desenho inteligente da matriz de suporte e dos ligandos de ��-dicetona que est��ao coordenados ao i��ao met��alico. Quando processados como filmes, este term��ometro permite o mapeamento de temperaturas com resolu��c��ao espacial 1.8 ��m. A racionaliza��c��ao da depend��encia de temperatura ��e uma ferramenta ��util para desenvolver term��ometros que operam em gamas de temperatura espec����ficos (e.g. gama de temperatura fisiol��ogica, 290-340 K) com sensibilidade acima de 0.5 % �� K���1. A combina��c��ao de esfor��cos de um grande n��umero de diversas disciplinas ir��a previsivelmente permitir o surgimento de term��ometros moleculares novos e sofisticados, preenchendo os principais requisitos das nanociencias.

Caracteriza����o e modifica����o de heteroestruturas de nitretos do grupo III

Os nitretos bin��rios semicondutores do grupo III, e respetivos compostos, s��o vastamente estudados devido �� sua poss��vel aplicabilidade em dispositivos optoeletr��nicos, tais como d��odos emissores de luz (LEDs) e LASERs, assim como dispositivos para a eletr��nica de elevadas temperatura, pot��ncia e frequ��ncia. Enquanto se concretizou a comercializa����o na ��ltima d��cada de LEDs e LASERs recorrendo ao tern��rio In1-yGayN, estudos das propriedades fundamentais estruturais e ��ticas, assim como de t��cnicas de processamento no desenvolvimento de novas aplica����es de outros tern��rios do grupo III-N encontram-se na sua fase inicial. Esta tese apresenta a investiga����o experimental de filmes finos epitaxiais de Al1-xInxN crescidos sobre camadas tamp��o de GaN e de Al1-yGayN e o estudo do recozimento e implanta����o de super-redes (SL) compostas por pontos qu��nticos de GaN (QD) envolvidos por camadas de AlN. Apesar do hiato energ��tico do Al1-xInxN poder variar entre os 0,7 eV e os 6,2 eV e, por isso, numa gama, consideravelmente superior �� dos tern��rios Al1-yGayN e InyGa1-yN, o primeiro �� o menos estudado devido a dificuldades no crescimento de filmes com elevada qualidade cristalina. �� efetuada, nesta tese, uma caracteriza����o estrutural e composicional de filmes finos de Al1-xInxN crescidos sobre camadas tamp��o de GaN e de Al1-yGayN usando t��cnicas de raios-X, feixe de i��es e de microscopia. Mostra-se que o Al1-xInxN pode ser crescido com elevada qualidade cristalina quando a epitaxia do crescimento se aproxima da condi����o de rede combinada do Al1-xInxN e da camada tamp��o (GaN ou Al1-yGayN), isto ��, com conte��do de InN de ~18%, quando crescido sobre uma camada de GaN. Quando o conte��do de InN �� inferior/superior �� condi����o de rede combinada, fen��menos de relaxa����o de tens��o e deteriora����o do cristal tais como o aumento da rugosidade de superf��cie prejudicam a qualidade cristalina do filme de Al1-xInxN. Observou-se que a qualidade dos filmes de Al1-xInxN depende fortemente da qualidade cristalina da camada tamp��o e, em particular, da sua morfologia e densidade de desloca����es. Verificou-se que, dentro da exatid��o experimental, os par��metros de rede do tern��rio seguem a lei emp��rica de Vegard, ou seja, variam linearmente com o conte��do de InN. Contudo, em algumas amostras, a composi����o determinada via espetrometria de retrodispers��o de Rutherford e difra����o e raios-X mostra valores discrepantes. Esta discrep��ncia pode ser atribu��da a defeitos ou impurezas capazes de alterar os par��metros de rede do tern��rio. No que diz respeito ��s SL dos QD e camadas de AlN, estudos de recozimento mostraram elevada estabilidade t��rmica dos QD de GaN quando estes se encontram inseridos numa matriz de AlN. Por implanta����o i��nica, incorporou-se eur��pio nestas estruturas e, promoveu-se a ativa����o ��tica dos i��es de Eu3+ atrav��s de tratamentos t��rmicos. Foram investigados os efeitos da intermistura e da relaxa����o da tens��o ocorridos durante o recozimento e implanta����o nas propriedades estruturais e ��ticas. Verificou-se que para flu��ncias elevadas os defeitos gerados por implanta����o s��o de dif��cil remo����o. Contudo, a implanta����o com baixa flu��ncia de Eu, seguida de tratamento t��rmico, promove uma elevada efici��ncia e estabilidade t��rmica da emiss��o vermelha do i��o lantan��deo incorporado nos QD de GaN. Estes resultados s��o, particularmente relevantes, pois, na regi��o espetral indicada, a efici��ncia qu��ntica dos LEDs convencionais de InGaN �� baixa.

Lanthanide oxide and phosphate nanoparticles for thermometry and bimodal imaging

Nesta tese relatam-se estudos de fotoluminesc��ncia de nanopart��culas de ��xidos e fosfatos dopados com i��es trivalentes de lantan��deos, respectivamente, nanobastonetes de (Gd,Eu)2O3 e (Gd,Yb,Er)2O3 e nanocristais de (Gd,Yb,Tb)PO4, demonstrando-se tamb��m aplica����es destes materiais em revestimentos inteligentes, sensores de temperatura e bioimagem. Estuda-se a transfer��ncia de energia entre os s��tios de Eu3+ C2 e S6 dos nanobastonetes Gd2O3. A contribui����o dos mecanismos de transfer��ncia de energia entre s��tios para o tempo de subida 5D0(C2) �� descartada a favor da relaxa����o directa 5D1(C2) 5D0(C2) (i.e., transfer��ncia de energia entre n��veis). O maior tempo de decaimento do n��vel 5D0(C2) nos nanobastonetes, relativamente ao valor medido para o mesmo material na forma de microcristais, �� atribu��do, quer �� exist��ncia de espa��os livres entre nanobastonetes pr��ximos (factor de enchimento ou frac����o vol��mica), quer �� varia����o do ��ndice de refrac����o efectivo do meio em torno dos i��es Eu3+. A dispers��o de nanobastonetes de (Gd,Eu)2O3 em tr��s resinas epoxi comerciais atrav��s da cura por UV permite obter nanocomp��sitos epoxi- (Gd,Eu)2O3. Relatam-se estudos cin��ticos e das propriedades t��rmicas e de fotoluminesc��ncia destes nanocomp��sitos. Estes, preservam as t��picas propriedades de emiss��o do Eu3+, mostrando o potencial do m��todo de cura por UV para obter revistimentos inteligentes e fotoactivos. Considera-se um avan��o significativo a realiza����o de uma nanoplataforma ��ptica, incorporando aquecedor e term��metro e capaz de medir uma ampla gama de temperaturas (300-2000 K) �� escala nano, baseada em nanobastonetes de (Gd,Yb,Er)2O3 (term��metros) cuja superf��cie se encontra revestida com nanopart��culas de ouro. A temperature local �� calculada usando, quer a distribui����o de Boltzmann (300-1050 K) do r��cio de intensidades da convers��o ascendente 2H11=2!4I15=2/4S3=2!4I15=2, quer a lei de Planck (1200-2000 K) para uma emiss��o de luz branca atribu��da �� radia����o do corpo negro. Finalmente, estudam-se as propriedades de fotoluminesc��ncia correspondentes ��s convers��es ascendente e descendente de energia em nanocristais de (Gd,Yb,Tb)PO4 sintetizados por via hidrot��rmica. A relaxividade (resson��ncia magn��tica) do 1H destes materiais s��o investigadas, tendo em vista poss��veis aplica����es em imagem bimodal (luminesc��ncia e resson��ncia magn��tica nuclear).

Metal-organic frameworks based on phosphonate linkers

During the last few decades, Metal-Organic Frameworks (MOFs), also known as Coordination Polymers, have attracted worldwide research attentions due to their incremented fascinating architectures and unique properties. These multidimensional materials have been potential applications in distinct areas: gas storage and separation, ion exchange, catalysis, magnetism, in optical sensors, among several others. The MOF research group at the University of Aveiro has prepared MOFs from the combination of phosphonate organic primary building units (PBUs) with, mainly, lanthanides. This thesis documents the last findings in this area involving the synthesis of multidimensional MOFs based on four di- or tripodal phosphonates ligands. The organic PBUs were designed and prepared by selecting and optimizing the best reaction conditions and synthetic routes. The self-assembly between phosphonate PBUs and rare-earths cations led to the formation of several 1D, 2D and 3D families of isotypical MOFs. The preparation of these materials was achieved by using distinct synthetic approaches: hydro(solvo)thermal, microwave- and ultrasound-assisted, one-pot and ionothermal synthesis. The selection of the organic PBUs showed to have an important role in the final architectures: while flexible phosphonate ligands afforded 1D, 2D and dense 3D structures, a large and rigid organic PBU isolated a porous 3D MOF. The crystal structure of these materials was successfully unveiled by powder or single-crystal X-ray diffraction. All multidimensional MOFs were characterized by standard solid-state techniques (FT-IR, electron microscopy (SEM and EDS), solid-state NMR, elemental and thermogravimetric analysis). Some MOF materials exhibited remarkable thermal stability and robustness up to ca. 400 ��C. The intrinsic properties of some MOFs were investigated. Photoluminescence studies revealed that the selected organic PBUs are suitable sensitizers of Tb3+ leading to the isolation of intense green-emitting materials. The suppression of the O���H quenchers by deuteration or dehydration processes improves substantially the photoluminescence of the optically-active Eu3+-based materials. Some MOF materials exhibited high heterogeneous catalytic activity and excellent regioselectivity in the ring-opening reaction of styrene oxide (PhEtO) with methanol (100% conversion of PhEtO at 55 ��C for 30 min). The porous MOF material was employed in gas separation processes. This compound showed the ability to separate propane over propylene. The ionexchanged form of this material (containing K+ cations into its network) exhibited higher affinity for CO2 being capable to separate acetylene over this environment non-friendly gas.

Post-synthetic modification of metal���organic frameworks

Post-synthetic modification (PSM) of metal-organic frameworks encompassing the chemical transformation of the linker present is a promising new route for engineering optical centres and tuning the light emission properties of materials, both in the visible and in the near infrared (NIR) spectral regions. Here, PSM of isoreticular metal-organic framework-3 (IRMOF-3) with ethyl oxalyl monochloride, ethyl acetoacetate, pentane-2,4-dione, 3-(2- hydroxyphenyl)-3-oxopropanal, 2-chloroacetic acid, glyoxylic acid, methyl vinyl ketone and diethyl (ethoxymethylene)malonate followed by chelation of trivalent lanthanide ions afforded intriguing near infrared (Nd3+) and visible (Eu3+, Tb3+) light emitters. IRMOF-3 was used as a case in point due to both its highly porous crystalline structure and the presence of non-coordinating amino groups on the benzenedicarboxylate (bdc) linker amenable to modification. The materials were characterised by elemental analysis, powder X-ray diffraction, optical, scanning and transmission electron microscopy, Fourier transform infrared spectroscopy, and liquid and solid-state nuclear magnetic resonance. The solid-state luminescence properties of Ln-modified-IRMOF-3 were investigated at room temperature. The presence of the bdc aromatic ring, ����� diketonate and oxalate enhanced the Ln3+ sensitization via ligand-to-metal energy transfer (anthena effect). As far as photocalysis is concerned, we have synthesized metal���organic frameworks (Cr-MIL-125-AC, Ag-MIL-125-AC) by a green method (solid���vapors reactions). The resulting functionalized materials show a photocatalytic activity for methylene blue degradation up to 6.52 times larger than that of the commercial photocatalyst hombikat UV-100. These findings open the door for further research for improving the photocatalytic performance of metal-organic frameworks.

A pyrophosphate-responsive gadolinium(III) MRI contrast agent

This study shows that the relaxivity and optical properties of functionalised lanthanide-DTPA-bis-amide complexes (lanthanide=Gd3+ and Eu3+, DTPA=diethylene triamine pentaacetic acid) can be successfully modulated by addition of specific anions, without direct Ln3+/anion coordination. Zinc(II)-dipicolylamine moieties, which are known to bind strongly to phosphates, were introduced in the amide ���arms��� of these ligands, and the interaction of the resulting Gd���Zn2 complexes with a range of anions was screened by using indicator displacement assays (IDAs). Considerable selectivity for polyphosphorylated species (such as pyrophosphate and adenosine-5���-triphosphate (ATP)) over a range of other anions (including monophosphorylated anions) was apparent. In addition, we show that pyrophosphate modulates the relaxivity of the gadolinium(III) complex, this modulation being sufficiently large to be observed in imaging experiments. To establish the binding mode of the pyrophosphate and gain insight into the origin of the relaxometric modulation, a series of studies including UV/Vis and emission spectroscopy, luminescence lifetime measurements in H2O and D2O, 17O and 31P���NMR spectroscopy and nuclear magnetic resonance dispersion (NMRD) studies were carried out.

INVESTIGATIONS ON THE SOLVENT EXTRACTION AND LUMINESCENCE OF LANTHANOIDS WITH MIXTURES OF HETEROCYCLIC ��- DIKETONE S AND VARIOUS NEUTRAL OXO-DONORS

The thesis entitled ��� Investigations on the solvent extraction and luminescence of lanthanoids with mixtures of heterocyclic ��-diketone S and various neutral oxo-donors��� embodies the results of investigations carried out on the solvent extraction of trivalent lanthanoids with various heterocyclic ��-diketones in the presence and absence of neutral oxo-donors and also on the luminescent studies of Eu3+-heterocyclic ��-diketonate complexes with Lewis bases. The primary objective of the present work is to generate the knowledge base, especially to understand the interactions of lanthanoid-heterocyclic ��-diketonates with various macrocyclic ligands such as crown ethers and neutral organophosphorus extractants , with a view to achieve better selectivity. The secondary objective of this thesis is to develop novel lanthanoid luminescent materials based on 3-phenyl-4-aroyl-5-isoxazolones and organophosphorus ligands, for use in electroluminescent devices. In the beginning it describes the need for the development of new mixed-ligand systems for the separation of lanthanoids and the development and importance of novel luminescent lanthanoid- ��-diketonate complexes for display devices. The syntheses of various para substituted derivatives of 4-aroyl-5-isoxazolones and their characterization by various spectroscopic techniques are described. It also investigate the solvent extraction behaviour of trivalent lanthanoids with 4-aroyl-5-isoxazolones in the presence and absence of various crown ethers such as 18C6, DC18C6, DB18C6 and B18C6. Elemental analysis, IR and H NMR spectral studies are used to understand the interactions of crown ethers with 4-aroyl-5-isoxazolonate complexes of lanthanoids. The synergistic extraction of trivalent lanthanoids with sterically hindered 1-phenyl-3-methyl-4-pivaloyl-5-pyrazolone in the presence of various structurally related crown ethers are studied. The syntheses, characterization and photyphysical properties of Eu3+-4-aroyl-5-isoxazolonate complexes in the presence of Lewis bases like trictylphosphine oxide or triphenylphosphine oxide were studied.