Navegando por Assunto "Espectroscopia Raman"

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Acesso aberto (Open Access)
Crescimento e caracterização dos cristais de sulfato de níquel hexahidratado dopados com íons [MnH2O]2+ e com sulfato de magnésio heptahidratado
(Universidade Federal do Pará, 2011) FERREIRA JÚNIOR, Messias de Nazaré Guimarães; REMÉDIOS, Cláudio Márcio Rocha; http://lattes.cnpq.br/7146076994037490
In this work, manganese ions doped nickel sulphate crystals (NSH:Mn) and magnesium ion doped nickel sulphate crystals (NMgSH) were grown and later characterized by X-ray diffraction and Raman spectroscopy techniques. The results obtained showed that the doped crystals possess a structure very similar to that of the pure nickel sulphate crystal (NSH), with an anisotropic deformation in the unit cell dimensions compared to the pure crystal, undergoing expansion in unit. The aim of the present study was to grow two new single crystals of good optical quality to be used as optical bandpass filters. Nickel sulfate hexahydrate (NHS) crystals are known to possess an optical transmission spectrum which has attracted much attention because it presents two regions with high transmission efficiency of approximately 80%, the first region being between 200 and 350 nm and the second between 400 and 600 nm, and a high absorption efficiency in other regions of the UV-VIS spectrum. A light transmission spectrum with these characteristics is similar to an optical filter. Termogravimetric (TGA) analyses were carried out for pure and doped crystals. The obtained decomposition temperature of NSH was found to be 73 °C while that NSH: Mn and NMgSH crystals present values of 82 ° C and 86 C respectively. As can be easily perceived, the thermal stability of crystals with Mn or Mg ions in their structures is significantly higher. The transmission band between 200 and 350 nm in the optical spectrum of NSH was found to be narrower in the transmission spectrum of the doped crystal thus restricting the region of the spectrum known as UVA.
Acesso aberto (Open Access)
Medidas de espectroscopia Raman em cristais KDP e Nanotubos de Carbono: implementação da técnica
(Universidade Federal do Pará, 2008-08-29) FERREIRA, Marcel Luiz Rodrigues; REMÉDIOS, Cláudio Márcio Rocha; http://lattes.cnpq.br/7146076994037490; MOREIRA, Sanclayton Geraldo Carneiro; http://lattes.cnpq.br/7312223977002681
Currently, physicist have developed new techniques for characterization materials, mainly in the field of new materials that are being produced from existing materials such as glass, ceramics, polymers, semiconductor and superconductor materials, magnetic materials, etc. In that line, the Group of Physic of materials of Amazon has acquired new techniques for material characterization and this work is the beginning of the implantation of Raman spectroscopy technique. In this work, we used sample of KH2PO4 crystals (KDP) and carbon single wall nanotube (SWNT). The KDP was chosen because their spectra are well-known and their preparation quite simple. The KDP pure or doped is still researched due have a ferroelectric transition and their several applications in laser, sensors, second and third harmonic generation. SWNT was used in this work because are materials of great scientific and technological interest with applications in nanotechnology such as transistor, diode. KDP samples were submitted uniaxial pressure and high temperatures to investigated possible phase transition. Both decomposition and phase transition was observed through Raman spectra of KDP. In the SWNT Raman spectra was identified well known D and G bands. The results support implantation of Raman spectroscopy in the Laboratory of spectroscopy of UFPA.
Acesso aberto (Open Access)
Síntese e caracterização de hidróxidos duplos lamelares a partir da lama vermelha
(Universidade Federal do Pará, 2011-08-30) CUNHA, Márcia Valéria Porto de Oliveira; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568; http://lattes.cnpq.br/6527800269860568
The adsorption is a process in which solids of natural or synthetic origin are used in metal retention, it is an alternative method for wastewater treatment, because combines low cost with high capacity to retain metals. The use of lamellar double hydroxides obtained from the red mud as adsorbent has the advantage of not produce a new generation of residue after the adsorption stage. This study was divided into four parts, with the following goals: synthesize and characterize HDLs formed from the red mud; investigate the anions that are part of the interlayer structure; investigate the ions incorporated into the structure and thermal stability; evaluate the adsorption capacity of HDLs through the removal of ion Cr(VI) in aqueous solution. For the synthesis and characterization of the LDHs, six experiments were performed. The following variables were studied: dripping time (3, 5 and 7h); hydrothermal bath time (5, 10, 20, 30 and 60 days), hydrothermal bath temperature; molar ratio and pH. This study showed that the LDHs formed have good crystallinity, the unit cell parameters a and c and the basal spacing values are similar to those found in the literature. For the investigation of the intercalated anions, molar ratios (M3+ / M2++M3+) close to 1:1were used. No precautions have been taken to avoid contact with atmospheric CO2, therefore some carbonate ions were introduced into the interlayer space. The LDH synthesized at room temperature (298 K), favored the intercalation of carbonate anion in the interlayer space. It occurs probably due the capture of CO2 from the atmosphere. The LDH synthesized at a temperature of 330 K, favored the intercalation of the anion chloride in the interlayer space. The intercalated ions in the structure were investigated using different cation ratios (MII / MII + MIII). The LDH with molar ratio Mg2+ / (Fe3+ + Al3+) higher were more crystalline and shown higher basal spacing values. The decomposition of LDHs occurred in three steps. The first and second step (25-100 °C and 100-235 °C) involve the loss of adsorbed and intercalated water, respectively. In the third step (235-410 °C) occurs dehydroxylation and decomposition of anions in the lamellae. A fourth stage of decomposition can be suggested here. It corresponds to the loss of volatile anionic species (Cl-, CO3 2-) or non-volatile species in which the anions are included by the formation of mixed metal oxides. For the samples synthesized from red mud, the following order of increasing thermal stability can be proposed: LV1> LV3 and LV4> LV2. LDHs were synthesized in the laboratory and its systematic Cr(VI) adsorption behaviour was studied by means of batch experiments. The effect of the parameters pH, concentration of Cr(VI) and the molar ratio MII/MII are here reported. The optimum pH and molar ratio required for maximum adsorption were found to between pH 4.0 – 6.0 and ratio between 3:1 – 4:1, respectively.