Catalytic Epoxidation and Sulfoxidation Activity of a Dioxomolybdenum(VI) Complex Bearing a Chiral Tetradentate Oxazoline Ligand

A dioxomolybdenum(vi) complex bearing a tetradentate anionic N,O oxazoline ligand with four stereocenters has been studied as a catalyst in the liquid-phase epoxidation of 17 different aliphatic and aromatic olefins (including prochiral, racemate or pure enantiomers) using tert-butyl hydroperoxide as the oxidant. Epoxide selectivities of up to 100% and variable epoxide yields (3–100% within 24 h) were obtained. Although the complex generally exhibited low or no chiral induction ability, diastereoselectivity was significant in some cases (in the reaction of limonene, for example). Kinetic studies and recycling tests with the substrates cis-cyclooctene and trans-β-methylstyrene showed that the catalyst is stable and reusable, and recycling is facilitated by immobilization of the complex in a room temperature ionic liquid. Preliminary results show that the complex may have a broad substrate scope, not only for olefin epoxidation, but also for the dehydrogenation of alcohols to carbonyl compounds and the sulfoxidation of sulfides to sulfoxides.     

Nitrous oxide emissions from an Uruguayan argiudoll under different tillage and rotation treatments

Lack of local data limits estimation of nitrous oxide (N₂O) emissions from different land uses of Uruguay. As a first step towards obtaining local information, we measured from August 2003 to September 2004 N₂O fluxes from a rotation-by-tillage experiment established in 1993 and from a nearby natural pasture (NP). Nitrous oxide emission rates were measured on an event-driven basis by using the closed chamber technique with six replicates per treatment. Fluxes varied considerably with time and the higher rates (more than 30 g N ha⁻¹ day⁻¹) were generally associated with periods of high soil water content, high temperature, and/or decreasing soil nitrate. We could not identify, however, any statistically significant correlation between flux and these variables. Throughout the evaluation period, fluxes from crops or cultivated pastures tended to be higher than those from NP, but the effects of tillage (no-till and conventional tillage) or rotation (continuous tillage and rotation with pasture) were not consistent. The application of 112 kg N ha⁻¹ to barley did not increase N₂O fluxes probably due to a high fertilizer use efficiency caused by the recommended three-split application and by the lack of rain during this period. The annual cumulative flows of different treatments compared well with those estimated using IPCC methodology, but the high spatial and temporal variability observed in this one-year study indicate that further research is needed to obtain reliable data on N₂O fluxes from agricultural soils of Uruguay.     

Synthesis,characterization and compared reactivity of asymmetrical ansa-metallocenes

Rac and meso ansa-zirconocenes [Zr{1-Me₂Si(3-R-(η⁵-C₉H₅))(3-R′-(η⁵-C₉H₅))}Cl₂] (R = Et, R′ = H; R = Pr, R′ = H; and R = Et, R′ = Pr) 4–9 have been prepared by the reaction of ZrCl₄ with the corresponding dilithiated derivatives from the ligands {1-Me₂Si(3-R-(η⁵-C₉H₅))(3-R′-(η⁵-C₉H₅))} (R = Et, R′ = H 1; R = Pr, R′ = H 2; and R = Et, R′ = Pr 3) in diethyl ether/toluene at ?78 °C. The molecular structure of rac [Zr{1-Me₂Si(3-Et-(η⁵-C₉H₅))(3-Pr-(η⁵-C₉H₅))}Cl₂] 8 has been determined by single crystal X-ray diffraction studies, which show a pseudotetrahedral environment formed by the two chlorine ligands and two η⁵-coordinated indenyl ligands. The activity in homogeneous and heterogeneous polymerization is compared and discussed.     

Natural Brazilian Amazonic (Curauá) Fibers Modified with Polyaniline Nanoparticles

The surface of natural Brazilian amazonic fibers (curauá, Ananas erectifolius) was modified with polyaniline nanoparticles, through in situ preparation of polyaniline nanoparticles in presence of the curauá fibers. This allowed for a significant increase in the electrical conductivity of the fibers (≈2 500 times). As the electrical resistivity of the modified fibers is a function of the applied external pressure, the produced composites can be used as a cheap pressure‐sensing material. The modified materials were also characterized by FT‐IR, XPS and SAXS, and the obtained results were used to explain some of the observed characteristics of the materials.

     

Effect of SiC and Al2O3 particles on the electrodeposition of Zn, Co and ZnCo: II. Electrodeposition in the presence of SiC and Al2O3 and production of ZnCo–SiC and ZnCo–Al2O3 coatings

SiC or Al₂O₃ microsized particles were added to acid sulfate-based solutions for the electrodeposition of Zn, Co, and ZnCo. Initially, their effects on the electrochemical processes were evaluated. The Zn electrodeposition rate was increased in both SiC and Al₂O₃-loaded solutions. The Co electrodeposition rate was also increased by SiC. However, Al₂O₃ decreased it, especially at the beginning. Both SiC and Al₂O₃ influenced the electrodeposition of ZnCo positively at moderate loadings. The factors involved in producing ZnCo–SiC and ZnCo–Al₂O₃ composites were evaluated. ZnCo–SiC composites could be deposited with a higher [Co/Zn] ratio in the metal matrix than for pure ZnCo. In ZnCo–Al₂O₃, the [Co/Zn] ratio was smaller than in ZnCo and ZnCo–SiC. It was necessary to reduce the CoSO₄ concentration to improve the Al₂O₃ co-deposition. The variation in [Co/Zn] ratio could, in principle, be related to the effects of SiC and Al₂O₃ on the individual Zn and Co electrodeposition.     

Blue pigments based on CoxZn1−xAl2O4 spinels synthesized by the polymeric precursor method

The Co_xZn_1?xAl₂O₄ system (x = 0; 0.1; 0.3; 0.5; 0.7; 0.9 and 1) was synthesized by the polymeric precursor method and characterized by the techniques XRD, TG-DTA, IR, UV–vis and colorimetry. The XRD patterns displayed the characteristic peaks of the spinel structure and a good crystallinity. The DTA curves showed an exothermic peak corresponding to the enthalpy of the transition taking place at about 700 °C. The infrared spectra displayed vibrations at about 650, 550, 540, 520, 500, 490 cm^?1, which were ascribed to the spinel structure. The UV–vis spectra presented three bands at 550, 580 and 620 nm attributed to the Co²⁺ spin transitions in tetrahedral sites. The colorimetric data point out the formation of blue pigments, corresponding to highly negative values of b¹. The lightness, coordinate L¹, increases with the heat treatment temperature. These facts reveal that Co_xZn_1?xAl₂O₄ is a promising system that can be employed to obtain ceramic blue pigments.     

Clay minerals and iron oxides-oxyhydroxides as fingerprints of firing effects in a limestone monument

Different Portuguese limestones-Encarnadão, Amarelo de Negrais, Lioz and Gresoso-have been widely used as building materials and ornamental stones in the architecture of Lisbon (Portugal) area.The aim of the study of those materials was focused on fire-induced stone damage, mainly on identifying the thermal transformations of clay minerals and iron oxides-oxyhydroxides. Taking into account an applied component to the cultural heritage, a special attention was given to one of the most ancient Portuguese monuments — Lisbon Cathedral, specifically its cloister that was severely damaged by a fire that occurred right after the 1755 earthquake.A set of samples collected from outcrops were studied and subjected to artificial heating. The results were compared with those obtained from samples collected in the monument. XRD, SEM-EDS and ⁵⁷Fe Mössbauer spectroscopy were used. The < 2 µm fraction varies significantly between unheated (outcrop samples) and artificially heated samples, particularly in relation to iron oxides-oxyhydroxides. Kaolinite is the dominant clay mineral, followed by illite and smectite. Goethite is the iron oxyhydroxide characteristic of all studied lithotypes both in unheated samples and samples artificially heated to 250 °C. Encarnadão is the exception presenting hematite in those conditions. As firing temperature increases (300 °C–600 °C) disordered hematite appears at the expense of goethite, and smectite is no longer detected. Mössbauer spectra further reveal that Fe²⁺ in silicate minerals is fully oxidized at 600 °C but remains in the carbonate structure up to this temperature. The SEM-EDS analyses show that 2:1 clay minerals have Si and Al as main cations and minor amounts of K and Fe. It also shows that all the clay minerals and Fe-rich particles are always associated to the limestone porosity.. The present results show that the clay minerals, namely illite–smectite mixed-layer and smectite, can be used as indicators of stone provenance used in Lisbon Cathedral Cloister as well as fingerprints of the temperature achieved during the fire of Lisbon Cathedral that most likely was not higher than 350 °C.     

Biodiesel compatibility with carbon steel and HDPE parts

Compatibility of the new environmentally-friendly alternative of diesel engine fuels, biodiesel, with storage and engine part materials, is still an open issue. In this work, the interaction between three fuels (petroleum diesel and two types of biodiesel — soybean and sunflower) and two materials (carbon steel and high density polyethylene) used in storage and automotive tanks, is analyzed in detail. A wide set of characterization techniques was used to evaluate the changes in both solid and fluid materials, as weight change measurement, optical, scanning electron and atomic force (AFM) microscopies, Raman and FTIR spectroscopies, and differential scanning calorimetry. The AFM technique allowed detecting surface roughness and morphology changes in the metallic material following the trends in the weight losses. In the case of polymeric material, weight gain by fluid absorption occurred, being detected by the spectroscopic techniques. The biodiesel fuels underwent some ageing however this phenomenon did not affect the interaction between the biodiesel fuels and the substrates. The petrodiesel, which did not age, caused more significant degradation of the substrates.     

Development and characterization of PEEK/carbon nanotube composites

New poly(ether ether ketone) (PEEK) based composites have been fabricated by the incorporation of single-walled carbon nanotubes (SWCNTs) using melt processing. Their structure, morphology, thermal and mechanical properties have been investigated. Scanning electron microscopy observations demonstrated a more uniform distribution of the CNTs for samples prepared following a processing route based on polymer ball milling and CNT dispersion in ethanol media. Thermogravimetric analysis indicated a remarkable improvement in the thermal stability of the matrix by the incorporation of SWCNTs. Differential scanning calorimetry showed a decrease in the crystallization temperature with increasing SWCNT content, whilst no significant changes were observed in the melting of the composites. The crystallite size determined by X-ray diffraction decreased at high SWCNT loading, which is attributed to the spatial limitations on crystal growth by confinement within the CNT network. Dynamic mechanical analysis revealed an increase in the storage moduli, hence in the rigidity of the systems, with increasing SWCNT content. Their addition shifts the glass transition peak to higher temperatures due to the restriction in chain mobility imposed by the CNTs. Higher thermal stability and mechanical strength were found for composites with improved dispersion of the SWCNTs.     

Effects of ultrasound on suspended particles in municipal wastewater

The objective of this research is to explore the fundamental characteristics of how particles in wastewater respond to ultrasound, with an aim to improve wastewater disinfection. Particles of a predetermined size fraction and concentration were treated with varying doses of ultrasound at 20.3 kHz. Ultrasonic power transfer to the fluid was measured using calorimetry or acoustical measurements. Image analysis particle counting was used to measure the size distribution of particles before and after ultrasound treatment. The influence of three parameters: particle origin (raw wastewater or from the aeration basin of the activated sludge process), particle concentration, and particle size on the percentage of particle breakage after ultrasound treatment was compared. It was found that raw wastewater and aeration basin particles of the same size fraction (90-106 μm) responded to ultrasound in a similar way. Particle breakage was not affected by changes in particle concentration from 100 to 400 particles per mL. Larger wastewater particles (90-250 μm) were more susceptible to breakage than smaller ones (38-63 μm diameter). The percentage of particle breakage increased linearly with a logarithmic increase in the ultrasound energy density, that is the ultrasound energy delivered per unit volume of the sample (R² = 0.48-0.91). An expression that predicts the percent of particles broken as a function of ultrasound energy density is provided.