Odair Pastor Ferreira

Unveiling the structure and composition of titanium oxide nanotubes through ion exchange chemical reactions and thermal decomposition processes

Neste trabalho reportamos reacoes de troca ionica e decomposicao termica em nanotubos de oxido de titânio, obtidos pelo tratamento hidrotermico de TiO 2 e NaOH. Considerando os resultados obtidos, sugerimos uma nova composicao quimica para os nanotubos: Na 2 Ti 3 O 7 ·nH 2 O. Os resultados tambem indicam que a estrutura da parede dos nanotubos seria isoestrutural as lamelas observadas para o Na 2 Ti 3 O 7 bulk. Dependendo da natureza da lavagem (agua deionizada ou solucao acida) executada no nanotubo apos o tratamento hidrotermico a concentracao de ions Na + pode ser modificada atraves de um processo de troca ionica do Na + por H + . Tais resultados permitem sugerir a seguinte formula quimica geral para os nanotubos obtidos: Na 2-x H x Ti 3 O 7 ·nH 2 O (0≤ x ≤2), sendo x dependente das condicoes de lavagens. In this paper we report the ion exchange reactions and the thermal decomposition of titanium oxide nanotubes, obtained by hydrothermal treatment of TiO 2 and NaOH. Based on these results we propose a new composition for the as-prepared nanotubes as Na 2 Ti 3 O 7 ·nH 2 O. Our results also suggest that nanotube walls have structure similar to those observed in the layer of the bulk Na 2 Ti 3 O 7 . Depending on how the washing process is performed on the nanotubes (water or acid solutions) the Na + content can be modified via the exchange reaction of Na

Ecomateriais: desenvolvimento e aplicação de materiais porosos funcionais para proteção ambiental

Fundamental aspects of the conception and applications of ecomaterials, in particular porous materials in the perspective of green chemistry are discussed in this paper. General recommendations for description and classification of porous materials are reviewed briefly. By way of illustration, some case studies of materials design and applications in pollution detection and remediation are described. It is shown here how different materials developed by our groups, such as porous glasses, ecomaterials from biomass and anionic clays were programmed to perform specific functions. A discussion of the present and future of ecomaterials in green chemistry is presented along with important key goals.

Interaction of sodium titanate nanotubes with organic acids and base: chemical, structural and morphological stabilities

Este trabalho relata a interacao de nanotubos de titanato de sodio (Na-TiNT) com solucoes aquosas de acido benzoico, acido fenilfosfonico e anilina. Os Na-TiNT foram obtidos atraves do tratamento hidrotermico de TiO 2 em solucao aquosa de NaOH. Os resultados obtidos atraves de FTIR, XRD, TEM e analise elementar mostraram que a estabilidade quimica, estrutural e morfologica dos nanotubos esta relacionada a natureza quimica do meio (basico ou acido) e as condicoes de tratamento (temperatura e tempo de contato). A fase α-fenilfosfonato de titânio(IV) foi formada a partir da interacao dos Na-TiNT com acido fenilfosfonico; a quantidade da nova fase foi dependente do tempo de contato e sua cristalinidade da temperatura. Porem, TiO 2 ou nanotubo de titanato contendo H + foram obtidos, em funcao das condicoes de tratamento, a partir da interacao dos Na-TiNT com acido benzoico. Quando os Na-TiNT interagiram com a anilina nenhuma mudanca estrutural, morfologica ou composicional foi observada. This work reports the interaction of sodium titanate nanotubes (Na-TiNT) with aqueous solutions of benzoic and phenylphosphonic acids and of aniline. The Na-TiNT were obtained from hydrothermal treatment of TiO 2 in aqueous NaOH solution. The results obtained from FTIR, XRD, TEM and elemental analyses showed that the chemical, structural and morphological stability of the nanotubes is related to the medium (acidic or basic) and to the treatment conditions (temperature and contact time). A titanium(IV) α-phenylphosphonate phase was obtained from interaction between Na-TiNT and phenylphosphonic acid. The amount and crystallinity of the new phase were dependent of the contact time and temperature, respectively. On the other hand, TiO 2 or protonrich titanate nanotubes were formed, depending on treatment conditions, from interaction between Na-TiNT and benzoic acid. When Na-TiNT interacted with aniline, no chemical, morphological or compositional change was observed.

Vibrational and thermal properties of crystalline topiramate

Topiramate, a powerful anticonvulsant drug, was investigated by X-ray diffractometry, FT-Raman, FT-IR, TGA and DTA techniques as well as by DFT calculations. From this study it was possible to tentatively assign most of the normal vibrational modes of the crystal. Thermal analysis from room temperature to 900 oC shows that the material does not present any structural phase transition and that the decomposition occurs in a two-step exothermic process.

Effect of the reaction medium on the immobilization of nutrients in hydrochars obtained using sugarcane industry residues

In this study, nutrients were immobilized on the hydrochars obtained by hydrothermal carbonization (HTC) of a vinasse and sugarcane bagasse mixture, in the presence of acid, base and salt additives at temperatures of 150, 190 and 230°C. The increase in temperature caused higher immobilization of Ca, Mg, K, N, Cu, Mn, Zn, B, P and Fe in all hydrochars produced. H3PO4 and NaOH immobilized higher amounts of P, Mg and Mn, while Ca was immobilized in higher quantities in the presence of H3PO4 and (NH4)2SO4. The addition of H2SO4, H3PO4 and (NH4)2SO4 was responsible for an increased immobilization of P, N, Ca, Mg and K. The immobilization of B, not present in the starting raw material, was possible with the addition of H3BO3. The results showed that it is possible to alter the reaction medium to immobilize nutrients on hydrochars produced from vinasse and sugarcane bagasse, for agricultural applications.

Large-field electron imaging and X-ray elemental mapping unveil the morphology, structure, and fractal features of a Cretaceous fossil at the centimeter scale.

We used here a scanning electron microscopy approach that detected backscattered electrons (BSEs) and X-rays (from ionization processes) along a large-field (LF) scan, applied on a Cretaceous fossil of a shrimp (area ∼280 mm(2)) from the Araripe Sedimentary Basin. High-definition LF images from BSEs and X-rays were essentially generated by assembling thousands of magnified images that covered the whole area of the fossil, thus unveiling morphological and compositional aspects at length scales from micrometers to centimeters. Morphological features of the shrimp such as pleopods, pereopods, and antennae located at near-surface layers (undetected by photography techniques) were unveiled in detail by LF BSE images and in calcium and phosphorus elemental maps (mineralized as hydroxyapatite). LF elemental maps for zinc and sulfur indicated a rare fossilization event observed for the first time in fossils from the Araripe Sedimentary Basin: the mineralization of zinc sulfide interfacing to hydroxyapatite in the fossil. Finally, a dimensional analysis of the phosphorus map led to an important finding: the existence of a fractal characteristic (D = 1.63) for the hydroxyapatite-matrix interface, a result of physical-geological events occurring with spatial scale invariance on the specimen, over millions of years.

Carbon Nanotubes: From Synthesis to Genotoxicity

Massive industrial production of carbon nanotubes (CNTs) is increasing year after year, and it is urgent to address their safety-related issues. Due to their morphological similarities with asbestos fibers, which are classical carcinogenic materials, these CNTs have been considered as hazardous manufactured products by regulatory agencies. In this context, genotoxic effects of CNTs and the mechanisms proposed in current literature are reviewed and discussed in this chapter. Relevant aspects of preparation and physicochemical characterization of CNTs in toxicological context as well as the recent perspectives involving cytotoxicity assessment are also highlighted. Finally, this chapter aims to contribute to point out to a proactive discussion towards a responsible and sustainable development of nanotechnology lined up with environmental, health, and safety (EH&S) requirements.

Photoluminescence Enhancement of Titanate Nanotubes by Insertion of Rare Earth Ions in Their Interlayer Spaces

The optical properties of titanate nanotubes (TiNts) intercalated with rare earths (RE) ions were intensively investigated in this study. To prepare the nanomaterials, sodium titanate nanotubes (Na-TiNts) were submitted to ion exchange reactions with different rare earth elements (RE: Pr3+, Er3+, Nd3+, and Yb3+). To the best of our knowledge, it is the first time that these RE-TiNts were synthesized. All samples were characterized by Raman spectroscopy, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). Furthermore, the optical properties were examined using photoluminescence spectroscopy (PL) and UV-Vis-NIR absorption spectroscopy. The PL intensity (visible range) of the RE-TiNt samples showed a strong dependence when the temperature was decreased down to 20źK. This PL enhancement probably was promoted by electronic modifications in titanate layer band gap and/or interface charge transfers due to RE ions intercalation.

Carbon Nanotube Doped Tellurite Glasses

In the past it was observed that buck ball doped glasses showed enhanced optical nonlinearities. However, carbon nanotubes are much more stable than buck ball and should be a better choice for that purpose. Therefore we decided to investigate the possibility to produce carbon nanotubes doped tellurite glasses and measured their optical nonlinearities. Tellurite glasses already have a larger nonlinearity compared to silica, and other, glasses. We produced TeO2-ZnO tellurite family glasses doped with multi wall Carbon Nanotube (CNT). The CNTs acquired from Carbolex were vigorously mechanically mixed with the tellurite glass precursors and melted in platinum crucible around 650°C in a controlled atmosphere inside an electrical induction furnace. We used the lowest temperature possible and controlled atmosphere to avoid the CNT oxidation. The glass melt was cast in a stainless steel and thermally treated at 300°C for 5 hours to relieve internal stresses. The samples were than cutted and polished to perform the optical characterization. We measured refractive index and thermo physical properties, such as vitreous transition Tg, crystallization onset Tx and melting Tf temperatures. Raman spectroscopy showed the possible presence of CNTs.

Template conversion of MoO3 to MoS2 nanoribbons: synthesis and electrochemical properties

Hydrothermally synthesized α-MoO3 nanoribbons were converted to MoS2 whilst retaining the same morphology by a solid–gas reaction at 800 °C in a H2S/H2/N2 atmosphere. In order to keep the nanoribbon morphology from the oxide in the sulfide, it was crucial to have a H2S stream during the whole heating process. Thereby, the first layer of sulfide is formed as soon as the oxide is activated avoiding coalescence of the nanoribbons. Afterwards, the sulfidization takes place from the outer shell to the inner core of the nanoparticles. Both α-MoO3 and MoS2-NR were investigated for the electrochemical intercalation of lithium-ions. The electrochemical insertion and removal of lithium in the molybdenum oxide are accompanied by a change of color, which was measured by in situ UV-Vis. Spectroelectrochemical experiments showed a distinguished electrochromic behavior with a significant potential-dependent change in absorbance at 660 nm upon Li+ insertion. Analysis of in situ voltammetry revealed the presence of three active sites for lithium insertion in the MoO3-NRs, which are accompanied by only two chromophores in the same potential range. Voltammetric measurements of the MoS2 nanoribbons presented a reversible reduction of MoS2 to LixMoS2, followed by Mo and Li2S, which can be further reduced to Li and S at more negative potentials. Such sulfide materials are highly promising for lithium batteries. This template synthesis is a simple method to obtain high purity MoS2 nanoparticles with a controlled morphology of nanoribbons.