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Zacharakis A.,Technical University of Crete | Chatzisymeon E.,Technical University of Crete | Binas V.,Institute of Electronic Structure and Laser IESL | Frontistis Z.,Technical University of Crete | And 3 more authors.
International Journal of Photoenergy | Year: 2013

The removal of bisphenol A (BPA) under simulated solar irradiation and in the presence of either TiO2 or ZnO catalysts immobilized onto glass plates was investigated. The effect of various operating conditions on degradation was assessed including the amount of the immobilized catalyst (36.1-150.7 mg/cm2 for TiO2 and 0.5-6.8 mg/cm2 for ZnO), initial BPA concentration (50-200 g/L), treatment time (up to 90 min), water matrix (wastewater, drinking water, and pure water), the addition of H2O2 (25-100 mg/L), and the presence of other endocrine disruptors in the reaction mixture. Specifically, it was observed that increasing the amount of immobilized catalyst increases BPA conversion and so does the addition of H2O2 up to 100 mg/L. Moreover, BPA degradation follows first-order reaction kinetics indicating that the final removal is not practically affected by the initial BPA concentration. Degradation in wastewater is slower than that in pure water up to five times, implying the scavenging behavior of effluent's constituents against hydroxyl radicals. Finally, the presence of other endocrine disruptors, such as 17ethynylestradiol, spiked in the reaction mixture at low concentrations usually found in environmental samples (i.e., 100 g/L), neither affects BPA degradation nor alters its kinetics to a considerable extent. © 2013 Andreas Zacharakis et al.

Koutantou V.,Technical University of Crete | Kostadima M.,Technical University of Crete | Chatzisymeon E.,Technical University of Crete | Frontistis Z.,Technical University of Crete | And 3 more authors.
Catalysis Today | Year: 2013

The photocatalytic degradation of synthetic estrogen 17α- ethynylestradiol (EE2) in environmental samples was investigated. Zinc oxide immobilized onto a glass substrate was prepared and used as the photocatalyst, while radiation was provided by a solar simulator. EE2 in the range 50-200 μg/L was treated in various matrices, i.e. ultrapure water, wastewater and drinking water, and treatment efficiency was assessed as a function of photon flux, ZnO loading and addition of hydrogen peroxide. Degradation follows apparent first-order kinetics and increases with increasing photon flux (4.93·10-7-5.8·10-7 einstein/(L s)) and H2O2 concentration (up to 100 mg/L), while ZnO loading (1.2-16.3 mg) has a marginal effect. Reaction in ultrapure water is twice as fast as in wastewater (e.g. the respective apparent rate constants are 17.3·10-3 and 9.4·10-3 min-1 at maximum photon flux and 3.7 mg ZnO) due to the competition for oxidants between EE2 and the wastewater components (organic matter and ions). The catalyst retained most of its activity upon repeated use (i.e. 21 consecutive runs of 31.5 h duration) although it was partially dissolved in the liquid phase; leached zinc can trigger homogeneous reactions, thus contributing to the overall photocatalytic degradation. © 2012 Elsevier B.V. All rights reserved.

Snijkers F.,Institute of Electronic Structure and Laser IESL | Vlassopoulos D.,Institute of Electronic Structure and Laser IESL | Vlassopoulos D.,University of Crete
Rheologica Acta | Year: 2014

We present a critical assessment of the range of validity of the empirical Cox-Merz rule for a wide range of model entangled polymer samples with a well-defined molecular structure, from linear monodisperse and polydisperse polymers, to branched model polymers (i.e. stars, H-polymers, and combs) and blends of linear polymers of the same chemistry. We focus on melts and concentrated solutions. Overall, we find that the simple empirical rule is obeyed rather well for the investigated cases. As often reported in the literature, relatively small systematic failures occur with the steady viscosity being below the complex one at high rates for most polymers, with linear polydisperse polymers (with a polydispersity index of about 2) being a notable exception. For the latter polymers, the rule is obeyed identically within experimental error. More unusual failures, with the steady shear viscosity being higher than the complex viscosity, are found for branched polymers with more than one branch point. More specifically, these unusual failures are observed at very high branching levels, when the backbone of the polymer is being stretched at low rates due to the motion of the branch points. The extra stress coming for the stretch renders the steady viscosity higher than the complex one. Due to the well-characterized nature of the combs, we can state that failures of the latter type are only apparent when the branches comprise more than 70 % of the molecular structure of the comb. This estimation could serve as a rough guideline in applications, although it is only a necessary and not sufficient condition for these failures to occur. © 2014, Springer-Verlag Berlin Heidelberg.

Kiriakidis G.,Institute of Electronic Structure and Laser IESL | Kiriakidis G.,University of Crete | Binas V.,Institute of Electronic Structure and Laser IESL | Binas V.,University of Crete
Journal of the Korean Physical Society | Year: 2014

Mn-, Co-, and Mn-Co doped TiO2 ternary and quaternary semiconducting powder materials prepared by using the co-precipitation method and fully characterized by using x-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM - EDS) and UV- visible diffuse reflection spectroscopy were utilized for the photocatalytic degradation of methylene blue under visible light irradiation. These materials show a red shift and absorption in the visible region depending on the dopant type and concentration. These materials have proven to be effective as visible light photocatalysts. © 2014 The Korean Physical Society.

Kymakis E.,Technological Educational Institute of Crete | Stylianakis M.M.,Technological Educational Institute of Crete | Spyropoulos G.D.,Technological Educational Institute of Crete | Stratakis E.,Technological Educational Institute of Crete | And 3 more authors.
Solar Energy Materials and Solar Cells | Year: 2012

Spin coated single-walled carbon nanotubes (SWNTs) are incorporated in organic bulk heterojunction photovoltaic devices as the hole transport layer (HTL). The SWNTs films were repetitively spin coated with dichloroethane to various thicknesses, and were evaluated as the HTL in poly(3-hexylthiophene) (P3HT) and 1-(3-methoxy-carbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) photovoltaic devices. Insertion of a 12.2 nm thick SWNTs layer leads to power conversion efficiencies as high as 3.04%, compared to 1.16% and 2.84% for the devices without and with the traditional PEDOT:PSS as the HTL, respectively. © 2011 Elsevier B.V. All rights reserved.

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