Estudos de processos electroquímicos em solução

Dissertação de Doutoramento em Química apresentada à Faculdade de Ciências da Universidade do Port

Constructed wetlands with light expanded clay aggregates for agricultural wastewater treatment

Constructed wetlands (CWs) are receiving a renewed attention as a viable phytotechnology for treating agricultural wastewaters and for the removal of more specific pollutants, in particular recalcitrant ones. In this work, the performance of CW mesocosms using light expanded clay aggregates (LECA) as the bed's substrate and planted with Phragmites australis was investigated for treatment of olive mill wastewater (OMW), swine wastewater (SW) contaminated with oxytetracycline and water contaminated with herbicide MCPA (2-methyl-4-chlorophenoxyacetic acid). Both wastewaters (OMW and SW) initially presented high organic matter content and total suspended solids which were removed by the system with efficiencies higher than 80%. Removal of polyphenols in OMW and nitrogen compounds in SW also showed similar or higher efficiencies in comparison with other treatment systems reported in the literature. The antibiotic oxytetracycline was completely removed from SW within the assay period in unplanted LECA beds, but planted beds allowed a significantly faster removal. In regard to water contaminated with MCPA, the results showed that LECA has a large sorption capacity for this herbicide (removal efficiencies of 56-97%). In general, considerably higher pollutant removal efficiencies were obtained when plants were used (up to 28% higher). The results obtained are indicative that CWs with LECA as substrate may be an adequate option for agricultural wastewater treatment

Organic xenobiotics removal in constructed wetlands, with emphasis on the importance of the support matrix

Constructed wetlands (CWs) are increasingly popular as an efficient and economical alternative to conventional wastewater treatment processes for removal, among other pollutants, of organic xenobiotics. In CWs, pollutants are removed through the concerted action of their components, whose contribution can be maximized by careful selection of those components. Specifically for non-biodegradable organic pollutants, the materials used as support matrix of CWs can play a major role through sorption phenomena. In this review the role played by such materials in CWs is examined with special focus on the amount of research that has been conducted to date on their sorption properties relatively to organic compounds. Where available, the reports on the utilization of some of those materials on pilot or full-scale CWs are also recognized. Greatest interest has been directed to cheaper and widely available materials. Among these, clays are generally regarded as efficient sorbents, but materials originated from agricultural wastes have also gained recent popularity. Most available studies are lab-scale batch sorption experiments, whereas assays performed in full-scale CWs are still scarce. However, the available lab-scale data points to an interesting potential of many of these materials for experimentation as support matrix of CWs targeted for organic xenobiotics removal

A DFT study on the adsorption of benzodiazepines to vermiculite surfaces

Widespread use of pharmaceuticals such as benzodiazepines has been resulting over the last decades in the dissemination of residues of these compounds in the environment, and such fact has been raising increasing concern. The generally low efficiencies of conventional wastewater treatment processes for the removal of this type of pollutants demands for the development of alternative or complementary water and wastewater treatment technologies, among which adsorption processes have been gaining popularity, provided that cheap efficient adsorbents are found. Clay materials have been one of the popular choices in this regard. In the present study, quantumchemical calculations have been performed by periodic DFT using the projector augmented-wave (PAW) method to characterize the interactions of two benzodiazepine molecules, alprazolam and diazepam, with a surface of clay mineral, vermiculite. It was observed that both molecules interact strongly with the vermiculite surface, both through a water-bridge binding and by cation-bridge provided by the exchangeable Mg2+ cations of the vermiculite surface. The results point to an interesting potential of vermiculite to be used efficiently as filter medium to remove these pollutants from water and wastewater

Electro-oxidation of carbamazepine metabolites: Characterization and influence in the voltammetric determination of the parent drug

Abstract The electro-oxidation behavior of five important metabolites of carbamazepine (CBZ) and their potential influence on the voltammetric determination of the parent drug in biological fluids was investigated for the first time. This investigation was performed using cyclic voltammetry, in combination with controlled potential electrolysis and HPLC-DAD-MS analysis of oxidation products of these compounds. Using a sensitive glassy carbon electrode modified with multi-walled carbon nanotubes it was found that each metabolite produces a voltammetric response, that differs from the parent molecule and which can be used in its identification and to gain some insight about the electro-oxidation mechanisms of this class of molecules. Taking into account the HPLC-DAD-MS data, these electro-oxidation mechanisms were advanced and discussed. A voltammetric procedure for the determination of CBZ in human fluids was also been tested. Selecting the most appropriate experimental conditions was verified that the interference of each metabolite and their oxidation products on the voltammetric signal of CBZ may be neglected. The analytical performance of the proposed voltammetric procedure, as well as the correlation of its results with the results obtained from LC–MS, were very good

Structure and conformation of HIV fusion inhibitor peptide T-1249 in presence of model membranes: A molecular dynamics study

Fusion of the HIV envelope with the target cell membrane is a critical step of viral entry into the target cell. Several peptides based on the C-region of HIV gp41 protein have been used in clinical trials as possible HIV fusion inhibitors, this way controlling the progression of the infection. Some of them interact strongly with ordered membranes, which could be linked to their effectiveness. In this way, extensive molecular dynamics simulations (100 ns) were carried out to investigate the structure, conformational behavior and dynamics of HIV fusion inhibitor peptide T-1249 in water and in the presence of bilayers of 1-palmitoyl-2-oleyl-phosphatidylcholine (POPC) and POPC–cholesterol (1:1). Peptide properties such as secondary structure, degree of membrane interaction and rotational and translational dynamics were analyzed. It was found that the peptide has a helical conformation in solution. It adsorbs readily to the membrane surface and remains tightly bound, with highly impeded rotational motion, keeping the helical structure. Whereas very limited penetration is observed in POPC, in the ordered POPC/cholesterol system the peptide just rests on top of the headgroup region of the bilayer, parallel to the surface. These results are rationalized in relation to recent experimental observations

Mono(¿5-cyclopentadienyl)metal(II) Complexes with Thienyl Acetylide Chromophores: Synthesis, Electrochemical Studies, and First Hyperpolarizabilities

A series of mono(η5-cyclopentadienyl)metal- (II) complexes with nitro-substituted thienyl acetylide ligands of general formula [M(η5-C5H5)(L)(CC{C4H2S}nNO2)] (M = Fe, L = κ2-DPPE, n = 1, 2; M = Ru, L= κ2-DPPE, 2 PPh3, n = 1, 2; M = Ni, L = PPh3, n = 1, 2) has been synthesized and fully characterized by NMR, FT-IR, and UV−Vis spectroscopy. The electrochemical behavior of the complexes was explored by cyclic voltammetry. Quadratic hyperpolarizabilities (β) of the complexes have been determined by hyper-Rayleigh scattering (HRS) measurements at 1500 nm. The effect of donor abilities of different organometallic fragments on the quadratic hyperpolarizabilities was studied and correlated with spectroscopic and electrochemical data. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were employed to get a better understanding of the secondorder nonlinear optical properties in these complexes. In this series, the complexity of the push−pull systems is revealed; even so, several trends in the second-order hyperpolarizability can still be recognized. In particular, the overall data seem to indicate that the existence of other electronic transitions in addition to the main MLCT clearly controls the effectiveness of the organometallic donor ability on the second-order NLO properties of these push−pull systems