Morphological, Optical and Electrical Characterization of the Interfaces in Fullerene-Porphyrin Thin Films.

The role of the interfaces on the optoelectronical properties of porphyrin-fullerene composites has been studied by means of ultraviolet-visible (UV-Vis) and Raman spectroscopy, atomic force microscopy (AFM) and electric conductivity measurements. A simple method of synthesis of donor- acceptor complexes has been performed by subsequent deposition of C60 fullerene and tetraphenylporphyrin (H2TPP) thin films, using physical vapor deposition (PVD) on a (100) silicon substrate. UV-Vis spectra showed that the interaction of π-orbitals leads to a more ordering for the dipole moments arrangement and the π-orbitals overlapping between C60 and H2TPP molecules. Besides, Raman spectra presented intensity changes at 960 and 1000 cm-1, both related to the vibration of the pyrrole ring and the rocking of the H on the C atoms within the macrocycle. Therefore, it can be expected that the interface C60-H2TPP should have a main role in the electric response of the multilayer films. The measurements of surface conductivity indicated that interface has specific contribution, and the value of surface conductivity is enhanced by charge delocalization mechanisms occur by π-π stacking interactions. It was found that the transversal conductivity of 3-layer films was enhanced by a factor of 4 in comparison to 2-layer film, due to charge transfer mechanisms occur in the junctions that could extend the diffusion length of the charge carriers. Finally, the interface generated between C60 and H2TPP films, without any linking molecule, enhance charge transport mechanism through the films.

Removal of aqueous chromium and environmental CO2 by using photocatalytic TiO2 doped with tungsten.

Removal of hexavalent chromium was accomplished by using photocatalyst materials of TiO2 doped with tungsten oxide, environmental air as oxygen supply and white light as irradiation source. Dichromate anions in concentration ranges of 50 to 1000 µg/L were removed by means of aqueous dispersions of TiO2 doped with tungsten. The aqueous chromium analyses were performed by Differential Pulse Voltammetry technique. Additionally, mineralization of CO2 gas was promoted by the photocatalysis process, as was clearly shown by Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS) analyses obtained from the TiO2 samples recovered after photocatalytic experiments. Results of sample analyses by Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM) are presented and discussed.

Chemical elemental analysis of single acoustic-levitated water droplets by laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy is presented for trace element detection of liquid samples by analyzing a single droplet levitated by ultrasonic waves. A single liquid droplet is placed in the node of a standing acoustic wave produced by a uniaxial levitator for further chemical analysis. The acoustic levitator consists of a commercial Langevin-type transducer, attached to a concave mechanical amplifier, and a concave reflector. A micro-syringe was used to manually place individual liquid droplet samples in the acoustic levitation system. For chemical analysis, a laser-induced plasma is produced by focusing a single laser pulse on the levitated water droplet after it partially dries. The performance of the acoustic levitator on micron-sized droplets is discussed, and the detection of Ba, Cd, Hg, and Pb at parts per million (milligrams/liter) and sub-parts per million levels is reported. The process, starting from placing the sample in the acoustic levitator and ending on the chemical identification of the traces, takes a few minutes. The approach is particularly interesting in applications demanding limited volumes of liquid samples and relative simple and inexpensive techniques.

Differentiation of fibrotic liver tissue using laser-induced breakdown spectroscopy.

Hepatic cirrhosis is a major cause of morbidity and mortality worldwide due to hepatitis C, alcoholism and fatty liver disease associated with obesity. Assessment of hepatic fibrosis relies in qualitative histological evaluation of biopsy samples. This method is time-consuming and depends on the histopathologists' interpretation. In the last decades, non-invasive techniques were developed to detect and monitor hepatic fibrosis. Laser-induced breakdown spectroscopy (LIBS) is a good candidate for a real-time, independent and fast technique to diagnose hepatic fibrosis. In this work LIBS was employed to characterize rat liver tissues with different stages of fibrosis. Depth profiling measurements were carried out by using a nanosecond Nd:YAG laser operated at the fundamental wavelength and an echelle spectrometer coupled with an ICCD camera. Due to the soft nature of the samples, plasma conditions largely change between consecutives shots. Thus, a theoretically supported procedure to correct the spectral line intensities was implemented. This procedure allows the reduction of the intensities' dispersion from 67% to 12%. After the correction, the LIBS signal shows an enhancement in calcium intensity by a factor of three as the fibrosis progressed. Calcium is known to increase crosslinking of extracellular matrix proteins in the fibrous septa. Therefore, our result singles it out as a key participant in the hepatic fibrosis.

Determination of the refractive index of glucose-ethanol-water mixtures using spectroscopic refractometry near the critical angle.

A spectroscopic refractometer was used to investigate the dispersion curves of ethanol and D-glucose solutions in water near the critical angle; here, the reflectivity was measured using a white source. Dispersion curves were obtained in the 320-1000 nm wavelength range with a resolution better than 10(-4) for the refractive index, n. The differential refractive index is measured as a function of wavelength, and a simple expression is proposed to obtain the refractive index of the glucose-ethanol-water ternary system. Using this expression, combined with the experimental differential refractive index values, the concentrations of individual components can be calculated.

Air pollution and respiratory diseases in children in São Paulo, Brazil.

Air pollution in the huge conurbation of São Paulo, Brazil (13 million inhabitants) has been mapped from air quality monitoring stations. In three contrasted sample areas, children's respiratory health parameters were collected to assess the roles of poverty and poor housing against those of air pollution. Respiratory ill-health is clearly shown to vary with pollution levels and there is evidence that socio-economic conditions aggravate the problem.