Caracterização espectroscópica de coacervados dopados com íons terras raras

-Os coacervatos são sistemas muito utilizados em química de materiais, principalmente na obtenção de materiais híbridos. Um estudo recente demonstrou que estes materiais atuam como precursores de sistemas vítreos e que podem funcionar como filtros de absorção na região do visível 1. Neste trabalho foi proposta a obtenção e caracterização espectroscópica de materiais vítreos a partir da matriz de polifosfato de sódio. Foram produzidos coacervatos de cobalto (II) e níquel (II) em diferentes proporções P/M2+, e caracterizados por técnicas espectroscópicas (Raman e Absorção de Raios-X), visando obter informações que possam descrever detalhadamente as estruturas dos mesmos, bem como o papel desempenhado pelos íons metálicos no processo de coacervação. Os coacervatos foram obtidos a partir de soluções de polifosfato de sódio, (4,0M) e sais de cloretos de níquel e cobalto em diferentes proporções P/M2+, variando de 0,5 a 10. Após algum tempo da mistura, ocorre a formação de vesículas coloidais que posteriormente se separam em duas fases; uma rica em partículas coloidais (coacervato) e outra compreendendo o sobrenadante. Os dados de espectroscopia Raman para o coacervato de cobalto mostram uma diminuição do número de onda, principalmente para o modo vibracional de deformação angular O-P-O em proporções P/Co2+> 2. Verifica-se que para P/Co2+=2 o mesmo apresenta-se em 317 cm-1 e para P/Co2+=10 em 305 cm-1; isso implica que o mesmo modo apresenta sensibilidade considerável à medida que se varia a concentração do cloreto de cobalto. Por outro lado, o estiramento assimétrico PO2 sofre um aumento do número de onda; 1248 cm-1 em P/Co=2 e 1264 cm-1 em P/Co2+=8. Estes resultados estão coerentes com o quadro de formação do coacervato: à medida que mais íons metálicos estão presentes, os mesmos se ''ligam às cadeias polifosfáticas externamente, tornando assim menos permitidos os modos de deformação angular O-P-O. As medidas EXAFS (efetuadas no Laboratório Nacional de Luz Síncrotron-LNLS), nas bordas-K do Ni e Co, mostram que a primeira esfera de coordenação dos íons metálicos é composta pelos átomos de oxigênio do hexaaquo complexo. Além disso, uma contribuição em torno de 3.2 Å do átomo central é atribuída à presença de átomos de fósforo. Através da análise dos fatores Debye-Waller em função das razões P/M, para os pares M-O e M-P, revelaram importantes características do processo de coacervação. Fatores Debye-Waller mais baixos foram encontrados nos coacervatos com baixas concentrações de metal (P/M2+> 6). Nessa faixa de concentração, os íons metálicos apresentam-se presos em gaiolas formadas pelas cadeias polifosfáticas ''enroladas'' em torno do íon. Na região de concentração 2 6, os aumentos bruscos dos fatores de Debye-Waller podem ser atribuídos à saturação das gaiolas, quando os íons metálicos passam a ocupar sítios externos nas cadeias polifosfáticas, ligando cadeias adjacentes, dando origem ao processo de coacervação. Após a saturação desses sítios, em P/M2+ >2, os íons metálicos adicionais apresentam-se principalmente como complexos hidratados, e os fatores de Debye-Waller apresentam valores constantes com a concentração. Além disso, nas esferas M-O, os coacervatos de Co2+ apresentam valores do fator de Debye-Waller maiores que aqueles de Ni2+, refletindo a maior tendência higroscópica dos primeiros em relação aos segundos. Os resultados de espectroscopia Raman e os valores de Debye-Waller apresentam comportamentos coerentes: quanto maior a relação P/M, mais íons metálicos ocupam posições externas nas cadeias polifosfáticas, contribuindo assim para uma perturbação das características físicas e químicas do material

Síntese e caracterizações estruturais e espectroscópicas de vidros e vitrocerâmicas contendo partículas metálicas usando óxido de antimônio (III) como agente redutor

This Thesis deals with the preparation of glasses based on sodium polyphosphate, containing antimony (III) and copper (II) oxides. The presence of α-Sb2O3 reducing agent was responsible for redox processes: Cu 2+→ Cu+→ Cu0 during synthesis of the glasses at 1000°C. The results of X-ray absorption measurements near the K edge of Cu (XANES) and electronic spectroscopy provided valuable information on the presence of metallic particles in glasses with nanometric dimensions. This result shows the possibility of obtaining metallic Cu nanoparticles during the melting step of glass preparation, without the need for posterior treatments. The synthesis of the different crystal phases of antimony (III) oxide, i.e., α-Sb2O3, α-Sb2O4, β-Sb2O4 and β-Sb2O3, through different isothermal treatments enabled the study through Raman spectroscopy and X-ray Diffraction. The ternary composition diagram for glass NaPO3-Sb2O3-CuO shows the different regions of vitreous domain. The spectroscopic study of glasses (0.9-x)NaPO3- xSb2O3-0,1CuO, containing Cu nanoparticles doped with 0.5 mol% of Er2O3 was realized by fluorescence spectroscopy using different exciting radiation: 532, 633 and 785 nm. The Raman mapping of these glasses showed the intensification of fluorescence of Er3+ ions, both the effect of changing the chemical environment around the Er3+ ion (crystallization) as the energy transfer from the excited surface plasmons for energy rare-earth ion levels (SEF - Surface-Enhanced Fluorescence). Additionally, glasses containing Cu nanoparticles showed satisfactory results of use as SERS substrates (Surface-Enhanced Resonance Spectroscopy), with the observed enhancement of the Raman signal of the vibrational modes of using phenylenediamine and the glass with x = 0.6 as substrate.O presente trabalho trata da preparação de vidros baseados em polifosfatos de sódio (NaPO3)n contendo óxidos de antimônio (III) e cobre (II), onde a presença do agente redutor α-Sb2O3 foi responsável pelos processos de oxi-redução: Cu2+→ Cu+→Cu0 durante a síntese dos vidros a 1000°C. Os resultados de medidas de absorção de Raios X próxima a borda K do Cu (XANES) e de espectroscopia Eletrônica forneceram informações valiosas sobre a existência de partículas metálicas nos vidros com dimensões nanométricas. Este resultado mostra a possibilidade de se obter nanopartículas metálicas de Cu0 durante a etapa de fusão dos vidros sem a necessidade de tratamentos térmicos dos materiais em temperaturas próximas a transição vítrea. A síntese de diferentes fases cristalinas do óxido de antimônio (III): α-Sb2O3, α-Sb2O4, β-Sb2O4 e β-Sb2O3, por meio de diferentes tratamentos isotérmicos possibilitou o estudo via espectroscopia Raman e Difração de Raios X por policristais destes compostos. O diagrama de composição ternário para os vidros (0,9-x)NaPO3-xSb2O3-0,1CuO mostra as diferentes regiões de domínio vítreo de formação de vidros estáveis. O estudo espectroscópico dos vidros (0,9-x)NaPO3-xSb2O3-0,1CuO contendo nanopartículas metálicas de Cu0 dopados com 0,5 mol% de Er2O3 foi realizado via espectroscopia de Fluorescência usando diferentes radiações excitantes: 532, 633 e 785 nm. O mapeamento Raman dos vidros mostrou a intensificação da fluorescência dos íons Er3+, tanto pelo efeito da mudança do ambiente químico ao redor do íon Er3+ (cristalização) quanto pela transferência de energia dos plasmons de superfície excitados para os níveis de energia do íon terra-rara (SEF – Surface-Enhanced Fluorescence). Além disso, vidros contendo nanopartículas metálicas de Cu0 apresentaram resultados satisfatórios quando a possibilidade de utilização como substratos SERS (Surface-Enhanced Resonance Spectroscopy), sendo observada a intensificação do sinal Raman dos modos vibracionais da o-fenilenodiamina usando o vidro x = 0,6 como substrato.CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Processo de preparação de vidros pela reação de coacervação de polifosfato em solução aquosa, em temperatura ambiente

The process of coacervation is through interaction between solutions of sodium polyphosphate (Graham's salt), (NaPO3)n and salts of different metals as: Na+, Ca2 +, Ni2 +, Co2+, Mn2+ among others. For the process of coacervation occurs in sometimes it is necessary the addition of organic solvents as methanol or ethanol, because these solvents reduce the dielectric constant of the solution leading to the formation of vesicles in aqueous solution. Use of coacervates for the production of glass by drying the coacervate (production of glass at room temperature) and then cooling the merger was explored. Structural and spectroscopic studies of the coacervates of cobalt (II) and nickel (II) were carried out by spectroscopic techniques of X-ray absorption in the region of the EXAFS and Raman spectroscopy providing important information on the first and second coordination spheres of metal ions, and the eminence given to the role played by them in the process of coacervation. In the production process of coacervates highlight the route of preparation by direct addition of methanol to the concentrated solution of (NaPO3)n. The materials obtained by different routes coacervation allowed us to obtain glassy materials with interesting features, according to the results of measurements of thermal analysis performed in these different materials. The melting process-cooling coacervates of calcium and sodium have also led to the formation of glasses with interesting thermal features. In addition special attention was given to the question of the coacervates compatibility of calcium and possible use as host matrices of drugs in the process of controlled release of drugs in humans. For this reason, vitamin C was incorporated into the coacervate of calcium in order to verify such aptitude pharmacology since these systems are prepared at room temperature under conditions favorable for the incorporation of different organic and inorganic substances in the structure of the material.O processo de coacervação se dá através da interação entre soluções aquosas de polifosfato de sódio (sal de Graham), (NaPO3)n, e sais de diferentes metais como: Na+, Ca2+, Ni2+, Co2+, Mn2+ entre outros. Para que o processo de coacervação ocorra, em alguns casos é necessário à adição de solventes orgânicos, como metanol ou etanol, visto que estes solventes reduzem a constante dielétrica da solução levando à formação de partículas coloidais em meio aquoso. A utilização de coacervatos para a produção de vidros seja pela secagem do coacervato (produção de vidros em temperatura ambiente) quanto pela fusão seguida de resfriamento foi explorada. Estudos estruturais e espectroscópicos dos coacervatos de Cobalto (II) e Níquel (II) foram realizados pelas técnicas espectroscópicas de absorção de Raios-X na região do EXAFS e Raman, fornecendo informações importantes sobre as primeiras e segundas esferas de coordenação dos íons metálicos, além do destaque dado ao papel desempenhado pelos mesmos no processo de coacervação. No processo de produção dos coacervatos destaca-se a rota de preparação através da adição direta de metanol à solução concentrada de (NaPO3)n. Os materiais obtidos pelas diferentes rotas de coacervação permitiram a obtenção de materiais com características vítreas interessantes, de acordo com os resultados das medidas de análises térmicas realizadas nestes diferentes materiais. O processo de fusão-resfriamento dos coacervatos de cálcio e sódio também conduziu à formação de vidros com características térmicas interessantes. Os coacervatos de cálcio e de sódio apresentam características vítreas, segundo medidas de Análise Térmica Diferencial (DTA). Mas, uma vez fundidos e resfriados dão origem a vidros que apresentam características térmicas interessantes, como por exemplo, baixas temperaturas de transição vítrea (Tg), cristalização (Tx) e fusão (Tf). Por outro lado, atenção especial foi dada à questão da biocompatilidade dos coacervatos de cálcio, e na possível utilização como matrizes hospedeiras de fármacos, no processo de liberação controlada de medicamentos no organismo humano. Para isso, a vitamina C foi incorporada ao coacervato de cálcio com objetivo de verificar tal aptidão farmacológica, visto que estes sistemas são preparados à temperatura ambiente em condições favoráveis para a incorporação de diferentes substâncias orgânico-inorgânicas na estrutura do material.CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Heavy metal oxide glass-ceramics containing luminescent gallium-garnets single crystals for photonic applications

Glass-ceramics containing rare earth gallium garnets were obtained using glass compositions as reactional medium. This work reports on the synthesis, and structural, morphological, and optical characterizations of Er3+ and Tm3+-doped Yb3Ga5O12 crystals prepared from controlled cooling of heavy metal oxide glass melts. Micrometric cubic crystals were obtained by controlling the cooling of a rare earth-supersaturated glassy composition melted at high temperature. Crystals with sizes ranging between 5 and 150 µm were formed into the glass matrix. A gallium garnet phase corresponding to space group Ia-3d was identified by X-ray diffraction and confirmed by Rietveld simulations. The morphology of crystals was studied by optical and scanning electron microscopies, while chemical elements were mapped by electron dispersive X-Ray spectroscopy. The glass phase was studied by XRD, thermal analysis and Raman spectroscopy. The optical properties of both glass and glass-ceramic materials were evaluated by UV–Vis and luminescence spectroscopies. Micro-luminescence measurements confirmed that rare earths were incorporated into the crystalline phase. Intense upconversion emissions of Er3+ (550 and 660 nm) and Tm3+ (800 nm) were observed when the glass-ceramics were pumped at 980 nm. These new glass-ceramics are excellent candidates for the development of photonic devices

Paramagnetic borotungstate glasses with high terbium concentration for magneto-optical applications

Glass system xTb2O3-40WO3-(60-x)B2O3, with x = 20; 22.5; 25 and 27.5 mol% were prepared by melting-quenching method. The samples were cut, polished and characterized by thermal, structural, optical, luminescent, magnetic and magneto-optical techniques aiming at applications in optical and magneto-optical devices. All terbium-containing samples exhibit magnetic response to neodymium magnets at room temperature. In addition, they feature thermal stability above 100 °C, wide transparency in the visible and near infrared region. Magnetic susceptibility measurements revealed the paramagnetic character of the terbium, with high Curie constants and antiparallel spin alignment. An ascending pattern in the Verdet constant was discerned as the concentration of Tb2O3 increased, culminating in a measurement of -124 rad·T−1·m−1 at 632.8 nm for the sample containing 27.5 mol% Tb2O3. This value closely approximates those observed in terbium-borogermanates glasses and single-crystal TGG, representing an alternative for the development of novel, cost-effective magneto-optical vitreous materials.Centre for functional and surface-functionalized glasse

Controlled formation of metallic tellurium nanocrystals in tellurite glasses using femtosecond direct laser writing

Tellurite glasses are considered a potential alternative for applications not achieved by SiO2-based glasses, presenting interesting optical properties, such as high linear and nonlinear refractive indexes, extended optical window, being also suitable for metallic nanoparticle growth, like Te0. When doped with sulfide species, it can benefit the reduction of Te4+ to Te0, which can be advantageous to synthesize in-situ chalcogenide nanoparticles and quantum dots. This work presents investigations on the reduction of Te4+ to Te0 in tellurite glasses doped with PbS and PbO/ZnS, and aims to control this redox process through the processing with pulsed fs-laser. Tellurite glass samples were synthesized by melt-quenching technique and the thermal and structural properties were explored by different techniques, such as DSC, Raman scattering spectroscopy and mapping experiment, TEM and SAED. Reduction of tellurium to Te0 nanocrystals into tellurite glass after laser irradiation was studied in detail and confirmed by the presence of bands at ~120 and 140 cm−1 in Raman spectroscopy and mapping, assigned to the Te–Te vibrational modes, which suggest that S2− induces in-situ Te4+ reduction. Moreover, quasi spherical tellurium nanoparticles were observed through TEM and confirmed their chemical nature and crystallization by SAED. The study of tellurium reduction in the vitreous matrix becomes particularly important and promising for some applications, since its reduction generates changes in the refractive index by precipitation of Te0 nanoparticles, allowing the fabrication of waveguides and as photosensitive material for tridimensional data storage

Tuning multicolor emission in AgNCs/Tm3+/Mn2+-doped fluorophosphate glasses

Herein we report the synthesis of highly-doped silver nanocluster in fluorophosphate glasses through the melting-quenching method in order to achieve sensitization with Tm3+ and Mn2+ ions. Blue and red emission belonging to Tm3+ (470 to 490 nm) and Mn2+ (550 to 750 nm) ions could be obtained via non-resonant excitation of Tm3+ and Mn2+. Slight decrease of the fluorescence decay times confirmed an energy transfer as a possible mechanism to explain the Tm3+ and Mn2+ emission. The composition of 5 mol% of AgNO3, 0.4 mol% of Tm2O3 and 0.2 mol% of MnF2 in our sample leads to distance between donor (silver nanoclusters) and acceptor (Tm3+-Mn2+) as short as 11 \uc5, which suggests that the main mechanism for blue and red emission from Tm3+ and Mn2+ is F\uf6rster Resonance Energy Transfer (FRET). The results presented here show that the studied material has potential application for multicolor generation as luminophore in white light emitting diodes (W-LED)

Investigating a new approach for magnetic ionic liquids: Dispersive liquid-liquid microextraction coupled to pyrolysis gas-chromatography-mass spectrometry to determine flame retardants in sewage sludge samples

This study addresses the analysis of emerging contaminants, often using chromatographic techniques coupled to mass spectrometry. However, sample preparation is often required prior to instrumental analysis, and dispersive liquid-liquid microextraction (DLLME) is a viable strategy in this context. DLLME stands out for its ability to reduce sample and solvent volumes. Notably, dispersive liquid-liquid microextraction using magnetic ionic liquids (MILs) has gained relevance due to the incorporation of paramagnetic components in the chemical structure, thereby eliminating the centrifugation step. A pyrolizer was selected in this work to introduce sample onto the GC column, since the MIL is extremely viscous and incompatible with direct introduction through an autosampler. This study is the first to report the use of a DLLME/MIL technique for sample introduction through a pyrolizer in gas chromatography coupled to mass spectrometry (GC-MS). This approach enables the MIL to be compatible with gas chromatography systems, resulting in optimized analytical and instrument performance. The analysis of polybrominated diphenyl ether flame retardants (PBDEs) was focused on the PBDE congeners 28, 47, 99, 100, and 153 in sewage sludge samples. The [P₆₆₆₁₄⁺]2[MnCl₄²⁻] MIL was thoroughly characterized using UV-Vis, Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, as well as thermal analysis. In the chromatographic method, a pyrolyzer was used in the sample introduction step (Py-GC-MS), and critical injection settings were optimized using multivariate approaches. Optimized conditions were achieved with a temperature of 220°C, a pyrolysis time of 0.60 min, and an injection volume of 9.00 μL. DLLME optimization was performed through central compound planning (CCD), and optimized training conditions were achieved with 10.0 mg of MIL, 3.00 μL of acetonitrile (ACN) as dispersive solvent, extraction time of 60 s, and volume of a sample of 8.50 mL. Precision was observed to range from 0.11% to 12.5%, with limits of detection (LOD) of 44.4 μg L−1 for PBDE 28, 16.9 μg L−1 for PBDE 47 and PBDE 99, 33.0 μg L−1 for PBDE 100 and 375 μg L−1 for PBDE 153. PBDE 28 was identified and analyzed in the sludge sample at a concentration of 800 μg L−1. The use of MIL in dispersive liquid-liquid microextraction combined with pyrolysis gas chromatography-mass spectrometry enables identification and quantification of PBDEs in sewage sludge samples at concentrations down to the µg L−1 level.This is a manuscript of the article Published as Rodrigues, Thais, Karen Chibana Ferreira, Guilherme Isquibola, Douglas Faza Franco, Jared L. Anderson, Josias Merib, and Paulo Clairmont Feitosa de Lima Gomes. "Investigating a new approach for magnetic ionic liquids: Dispersive liquid-liquid microextraction coupled to pyrolysis gas-chromatography-mass spectrometry to determine flame retardants in sewage sludge samples." Journal of Chromatography A (2024): 465038. doi: https://doi.org/10.1016/j.chroma.2024.465038. © 2024 Elsevier B.V. CC BY-NC-ND. Posted with Permission

Thermal and structural modification in transparent and magnetic germanoborate glasses induced by Gd2O3

A series of new transparent and magnetic germanoborate glasses in the system (100-x)[60GeO2–25B2O3–10Na2O–4Al2O3–1PbO] – (x) Gd2O3, with x = 0, 1, 2, 5, 10, 15 and 20 mol%, was prepared and studied with respect to their thermal and structural changes in the presence of Gd2O3. Based on Differential Scanning Calorimetre (DSC) analysis, a glass with 5% of Gd2O3 showed a high thermal stability, which progressively decreases for samples with higher content of Gd2O3. By the analysis of Raman and Fourier Transform Infrared (FTIR) spectra, it was possible to identify that by increasing the amount of Gd2O3, a progressive depolymerization of 6-membered Ge[IV] rings is promoted, concomitant with an increase of Ge[IV] tetrahedra units with non-briding oxygens. The structural analysis through the local-sensitive techniques EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure) showed that the short-range structural modification around the elements Ge and Gd3+ does not change with the addition of Gd2O3 and the presence of germanium four-fold coordination [GeIV] and Gd3+ states, respectively. A simulation of the coordination number (N), the interatomic distance (R) of Ge–O and Gd–O bonds and the Debye-Waller factor was also carried out. The microstructure, after crystallization, of the sample with 15 mol% of Gd2O3 was evaluated using optical and electron microscopes. Finally, the paramagnetic behaviour and ion probe quantification of Gd3+ ions were obtained based on magnetic susceptibility measurements