Dyes removal from water using low cost absorbents

In this study, the removal capacity of low cost adsorbents during the adsorption of Methylene Blue (MB) and Congo Red (CR) at different concentrations (50 and 100mg•L-1) was evaluated. These adsorbents were produced from wood wastes (cedar and teak) by chemical activation (ZnCl2). Both studied materials, Activated Cedar (AC) and activated teak (AT) showed a good fit of their experimental data to the pseudo second order kinetic model and Langmuir isotherms. The maximum adsorption capacities for AC were 2000.0 and 444.4mg•g-1 for MB and CR, respectively, while for AT, maximum adsorption capacities of 1052.6 and 86.4mg•g-1 were found for MB and CR, respectively. © Published under licence by IOP Publishing Ltd

Studies on honey from the Algarve in view of its valorization

Tese de dout., Química, Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2012Erasmus Mundus 2008-1022/002Several studies were conducted with different Portuguese honey samples from South area (Algarve) in view of exploiting its properties and increasing the commercial value of some types of honey. Initially, the effects of honey storage for long periods were evaluated in terms of physicochemical parameters and bioactivity (Chapter 3) and it was concluded that after three years most of the properties of honey remained unchanged except for the freshness indicators, which were, as expected, reasonably far from the regulated values. Several commercial samples of honey with different floral origins were subjected to the conventional studies, including melissopalynology pollen analysis, physiochemical and biological (antioxidant properties) analysis. Honey from strawberry tree (Arbutus unedo L.), a typical plant in Algarve, was the focus of this study. This kind of honey has low acceptability by consumers probably because of unawareness of its existence and/or of its beneficial biological properties. Also, it may not be an obvious preference, due to its exquisite bitter taste, thus being locally called “bitter honey” (Chapter 4). Artisanal bitter honey was compared with other commercial honeys that are appreciated by Portuguese consumers (Chapter 5). This research consisted in the study of the physicochemical parameters, bioactive compounds and sensorial evaluation; done in comparison with sunflower (Helianthus annuus) honey, french lavender (Lavandula stoechas) honey, orange blossom (Citrus spp.) honey and commercial strawberry tree honey. Finally, in the last stage of the work (Chapter 6), new methods for determination of botanical origin of honey were explored as potential alternatives to the traditional analysis method (melissopalynological). These non-invasive techniques namely electronic tongue, UV-Vis spectroscopy and Vis-NIR spectroscopy, were used with the help of multivariate analysis (principal component analysis, PCA), for the interpretation of data’s obtained with above techniques. It is hoped that this research will represent an enrichment of knowledge on honey from the Algarve and, especially for Arbutus unedo honey, it has been demonstrated that it has the characteristics of similar gourmet honey from Italy existing, therefore, the potential of increasing its commercial value, which would also be advantageous for the interior region of the Algarve where, since the Arab occupation, the strawberry tree is abundant

Zero-field Kondo splitting and quantum-critical transition in double quantum dots

Double quantum dots offer unique possibilities for the study of many-body correlations. A system containing one Kondo dot and one effectively noninteracting dot maps onto a single-impurity Anderson model with a structured (nonconstant) density of states. Numerical renormalization-group calculations show that while band filtering through the resonant dot splits the Kondo resonance, the singlet ground state is robust. The system can also be continuously tuned to create a pseudogapped density of states and access a quantum critical point separating Kondo and non-Kondo phases.Comment: 4 pages, 4 figures; Accepted for publication in Physical Review Letter

Spin relaxation rates in quasi-one-dimensional coupled quantum dots

We study theoretically the spin relaxation rate in quasi-one-dimensional coupled double semiconductor quantum dots. We consider InSb and GaAs-based systems in the presence of the Rashba spin-orbit interaction, which causes mixing of opposite-spin states, and allows phonon-mediated transitions between energy eigenstates. Contributions from all phonon modes and coupling mechanisms in zincblende semiconductors are taken into account. The spin relaxation rate is shown to display a sharp, cusp-like maximum as function of the interdot-barrier width, at a value of the width which can be controlled by an external magnetic field. This remarkable behavior is associated with the symmetric-antisymmetric level splitting in the structure.Comment: 4 figures, Submitted to Applied Physics Letter

Spatially resolved manipulation of single electrons in quantum dots using a scanned probe

The scanning metallic tip of a scanning force microscope was coupled capacitively to electrons confined in a lithographically defined gate-tunable quantum dot at a temperature of 300 mK. Single electrons were made to hop on or off the dot by moving the tip or by changing the tip bias voltage owing to the Coulomb-blockade effect. Spatial images of conductance resonances map the interaction potential between the tip and individual electronic quantum dot states. Under certain conditions this interaction is found to contain a tip-voltage induced and a tip-voltage independent contribution.Comment: 4 pages, 4 figure

Tuning hole mobility in InP nanowires

Transport properties of holes in InP nanowires were calculated considering electron-phonon interaction via deformation potentials, the effect of temperature and strain fields. Using molecular dynamics, we simulate nanowire structures, LO-phonon energy renormalization and lifetime. The valence band ground state changes between light- and heavy-hole character, as the strain fields and the nanowire size are changed. Drastic changes in the mobility arise with the onset of resonance between the LO-phonons and the separation between valence subbands.Comment: 4 pages, 4 figure