PHOTOINDUCED PROCESSES IN SUPRAMOLECULAR SYSTRMS FOR SOLAR ENERGY CONVERSION

Artificial photosynthesis, defined as the conversion of solar energy into fuels, could provide a solution to the problem of the intermittent avalaibility of sunlight, one of the key issues to overcome in order to implement widespread use of solar energy. Among the possible applications of artificial photosynthesis, particularly interesting are photochemical water splitting, since it represents a possible way to solar hydrogen generation, and the photocatalytic reduction of CO2 to CO, HCOOH, CH3OH or CH4, important industrial intermediates or fuels. In a biomimetic approach, a generic artificial photosynthetic device consists of an antenna system, a charge-separating reaction center, an oxidation catalyst and a reduction catalyst. Antenna systems absorb visible photons, thus converting them to electronic excitation energy which is then conveyed via energy transfer processes to the reaction center where it drives electron transfer processes leading to charge separation. The photogenerated electrons and holes provide to the catalysts the oxidizing and reducing equivalents necessary to drive redox reactions on a substrate. In this work, a number of systems proposed as possible components of an artificial photosynthetic device or as models for the investigation of related key processes are studied. The systems described here are designed organizing molecular components in spatially defined architectures, following the principles of supramolecular chemistry. In particular, Chapter 3 describes a triad for charge-separation obtained by selfassembling of a Ru-porphyrin electron donor, an Al-porphyrin as the photoexcitable chromophore and a naphtalenebisimide electron acceptor. The intrinsically asymmetric nature of triad systems required the development of assembling strategies based on molecular recognition between the subunits, implemented exploiting highly selective metalligand interactions. Photoinduced charge-separation was demostrated by a detailed photophysical and electrochemical characterization. In Chapter 4, a Sn-porphyrin component and a Ru-porphyrin component are combined in a series of tri-, penta- and heptanuclear supramolecular arrays. A number of photoinduced intercomponent electron-transfer processes, leading to a common chargeseparated state, could be identified by use of time-resolved UV-Vis absorption and emission spectroscopy and their kinetics rationalized in terms of standard electron-transfer theory. Chapter 5 describes a model complex of the [FeFe] hydrogenase enzyme active site, tested as a reduction catalyst for photochemical hydrogen production. High turnover numbers were obtained in a photocatalytic cycle using Ru(bpy)3 2+ as photosensitizer and ascobic acid as sacrificial electron donor. In Chapter 6, a kinetic study on [Ru4(μ-O)4(-OH)2(H2O)4(γ-SiW10O36)2]10-, a recently proposed Ruthenium Polyoxometalate catalyst for the oxygen-evolving side of water splitting, is presented. Hole transfer from photogenerated oxidants to the catalyst has been investigated by means of nanosecond laser flash photolysis, both in solution and at a sensitized TiO2 surface. The very fast rates observed open the possibility to include [Ru4(μ- O)4(-OH)2(H2O)4(γ-SiW10O36)2]10- in photochemical water splitting devices. Chapter 7 describes the photophysical investigation of supramolecular systems containing a Zn-porphyrin chromophore and the [fac-Re(CO)3(bpy)]+ fragment as components. Polypyridine-Re(I)-tricarbonyl complexes are known to catalyze CO2 reduction, opening the possibility to exploit them for photocatalysis. The results obtained provided guidelines for the realization of new adducts to be tested in photocatalytic cycles. A side-project in the field of molecular electronics is also reported in Chapter 8. Photoinduced electron transfer is demonstrated here as the working principle of a prototype photochromic switch for non-destructive read-out optical memory systems. The system proposed is composed of a diarylethene as photochromic unit and a perylene bisimide as fluorophore

Two-step growth mechanism of supported Co3O4-based sea-urchin like hierarchical nanostructures

The formation mechanism of Co3O4-based sea-urchin like nanostructures from Co-O-B layers is unveiled. In this process, promoted by oxidizing annealing, B plays a major role, inducing first a chemical reduction of Co and the formation of a metallic particle core. The growth of nano-needles from the particle surface occurs through outdiffusion and oxidation of Co from the metallic reservoir

Reflexões sobre o telejornalismo no horário nobre: um estudo comparativo do Jornal Nacional e do Jornal da Record

Este artigo tem como foco a comparação de dois importantes telejornais brasileiros que vão ao ar no horário nobre: Jornal Nacional, da Rede Globo, e Jornal da Record, da Rede Record. O objetivo principal deste estudo é analisar as especificidades individuais e comuns dos dois telejornais. Tomamos como suporte metodológico a análise do discurso. Analisamos a edição do dia 28 de maio de 2012 do JN e a edição do mesmo dia do J

Is contrast enhancement needed for diagnostic prostate MRI?

Prostate Imaging Reporting and Data System version 2 (PI-RADS v2) provides clinical guidelines for multiparametric magnetic resonance imaging (mpMRI) [T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI) and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI)] of prostate. However, DCE-MRI seems to show a limited contribution in prostate cancer (PCa) detection and management. In our experience, DCE-MRI, did not show significant change in diagnostic performance in addition to DWI and T2WI [biparametric MRI (bpMRI)] which represent the predominant sequences to detect suspected lesions in peripheral and transitional zone (TZ). In this article we reviewed the role of DCE-MRI also indicating the potential contribute of bpMRI approach (T2WI and DWI) and lesion volume evaluation in the diagnosis and management of suspected PCa

Towards the Development of a Z-Scheme FeOx/g-C3N4 Thin Film and Perspectives for Ciprofloxacin Visible Light-Driven Photocatalytic Degradation

Thermally synthesized graphitic carbon nitride (g-C3N4) over pulsed laser deposition (PLD) produced urchin-like iron oxide (FeOx) thin films were fabricated via in situ and ex situ processes. Materials characterisation revealed the formation of the graphitic allotrope of C3N4 and a bandgap Eg for the combined FeOx/g-C3N4 of 1.87 and 1.95 eV for each of the different fabrication strategies. The in situ method permitted to develop a novel petal-like morphology, whereas for the ex situ method, a morphological mixture between FeOx bulk and g-C3N4 was observed. Given the improved optical and morphological properties of the in situ film, it was employed as a proof of concept for the direct photocatalysis and photo-Fenton removal of ciprofloxacin antibiotic (CIP) under visible light irradiation. Improved photocatalytic activity (rate constant k = 8.28 × 10−4 min−1) was observed, with further enhancement under photo-Fenton conditions (k = 2.6 × 10−3 min−1), in comparison with FeOx + H2O2 (k = 1.6 × 10−3 min−1) and H2O2 only (k = 1.3 × 10−4 min−1). These effects demonstrate the in situ methodology as a viable route to obtain working heterojunctions for solar photocatalysis in thin-film materials, rather than the more common powder materials

In Stent Restenosis Predictors after Carotid Artery Stenting

Purpose. The long-term efficacy of carotid artery stenting is debated. Predictors of stent restenosis are not fully investigated. Our aim was to assess the incidence of long term restenosis after CAS and to identify some predictors of restenosis. Methods. We retrospectively selected 189 treated patients and we obtained the survival Kaplan-Meier curves for overall survival, for freedom from stroke or death and from restenosis. To correlate clinical, radiological, and procedural variables to stent restenosis, an univariate analysis was performed while to determine independent predictors of restenosis, a multivariate analysis was applied. Results. At 1, 3, and 5 years, the cumulative overall survival rate was 98%, 94%, and 92% with a cumulative primary patency rate of 87%, 82.5%, and 82.5%. The percentage residual stenosis after CAS and multiple stents deployment were independent predictors of restenosis, while diabetes and tumors are suggestive but not significant predictors of restenosis. Conclusions. In our CAS experience, encouraging long-term results seem to derive from both neurological event free rate and restenosis incidence. Adequate recanalization of the treated vessel is important to limit the development of stent restenosis. Multiple stents deployment, and with less evidence, diabetes, or neoplasms has to be considered to facilitate restenosis