Institute of Electronic Structure and Laser IESL

Irákleion, Greece

Institute of Electronic Structure and Laser IESL

Irákleion, Greece
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Kakavelakis G.,Technological Educational Institute of Crete | Del Rio Castillo A.E.,Italian Institute of Technology | Pellegrini V.,Italian Institute of Technology | Ansaldo A.,Italian Institute of Technology | And 6 more authors.
ACS Nano | Year: 2017

The development of large-scale production methods of two-dimensional (2D) crystals, with on-demand control of the area and thickness, is mandatory to fulfill the potential applications of such materials for photovoltaics. Inverted bulk heterojunction (BHJ) organic solar cell (OSC), which exploits a polymer-fullerene binary blend as the active material, is one potentially important application area for 2D crystals. A large ongoing effort is indeed currently devoted to the introduction of 2D crystals in the binary blend to improve the charge transport properties. While it is expected that the nanoscale domains size of the different components of the blend will significantly impact the performance of the OSC, to date, there is no evidence of quantitative information on the interplay between 2D crystals and fullerene domains size. Here, we demonstrate that by matching the size of WSe2 few-layer 2D crystals, produced by liquid-phase exfoliation, with that of the PC71BM fullerene domain in BHJ OSCs, we obtain power conversion efficiencies (PCEs) of ∼9.3%, reaching a 15% improvement with respect to standard binary devices (PCE = 8.10%), i.e., without the addition of WSe2 flakes. This is the highest ever reported PCE for 2D material-based OSCs, obtained thanks to the enhanced exciton generation and exciton dissociation at the WSe2-fullerene interface and also electron extraction to the back metal contact as a consequence of a balanced charge carriers mobility. These results push forward the implementation of transition-metal dichalcogenides to boost the performance of BHJ OSCs. © 2017 American Chemical Society.


Venieri D.,Technical University of Crete | Gounaki I.,Technical University of Crete | Binas V.,Institute of Electronic Structure and Laser IESL | Binas V.,University of Crete | And 4 more authors.
Applied Catalysis B: Environmental | Year: 2014

The beneficial properties of metal-doped titania nanoparticles with respect to wastewater disinfection under solar irradiation were investigated. Mn-, Co- and binary Mn/Co-doped TiO2 catalysts were prepared by means of a co-precipitation method and were subsequently assessed in terms of their potential to inactivate MS2 bacteriophage in slurry reactor under simulated and natural solar irradiation. Disinfection effectiveness was evaluated in relation to influential operating parameters, like catalyst type (Mn-, Co- and Mn/Co), dopant concentration (0.02-1molwt%), artificial and natural solar light, wavelength (i.e. >420nm) and photon flux (4.93-5.8×10-7 E/(Ls)). Metal doping led to considerable narrowing of the band gap and the spectral response of the catalysts extended well into the visible region. MS2 phage was readily inactivated in sewage samples under simulated solar irradiation in the presence of the prepared metal-doped catalysts. The latter proved to be superior to the commercial P25, under the current experimental conditions, resulting in an approximately 60% phage population decrease in almost 60min of simulated solar irradiation when initial MS2 concentration was 105 PFU/mL. Catalysts with the binary dopant exhibited the best photocatalytic activity in all cases, as almost 99% of MS2 population was eliminated in less than 20min of irradiation highlighting the fact that composite dopants induce a synergistic effect. The effect of different dopants concentration was apparent up to a certain limit. Disinfection follows a pseudo-first order kinetic rate. Retardation of the process by a factor 1.6-3.8 was recorded under natural solar light, based on the kinetic rate constants of inactivation curves which were within the range of 0.032-0.057min-1. The corresponding range for inactivation under simulated solar irradiation was 0.053-0.221min-1. Moreover, testing the Mn-, Co-, and binary Mn/Co doped TiO2 in the absence of UV light, they were considerably sensitized making clear that they can be activated in the visible part of the spectrum. © 2014 Elsevier B.V.


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.


Venieri D.,Technical University of Crete | Fraggedaki A.,Technical University of Crete | Kostadima M.,Technical University of Crete | Chatzisymeon E.,Technical University of Crete | And 6 more authors.
Applied Catalysis B: Environmental | Year: 2014

The present study deals with the inactivation of Escherichia coli and Klebsiella pneumoniae in water by means of heterogeneous photocatalysis under simulated solar irradiation. For this purpose, novel Mn-, Co- and Mn/Co-doped TiO2 catalysts were prepared. A straightforward, simple and inexpensive process has been developed based on a co-precipitation method for the synthesis of metal-doped catalysts, which were subsequently assessed in terms of their disinfection efficiency. The effect of various operating conditions, such as metal dopant (Mn-, Co- and Mn/Co), dopant concentration (0.02-1wt%), catalyst concentration (25-250mg/L), bacterial concentration (102-108CFU/mL), treatment time (up to 60min), toxic effects on bacteria and photon flux (4.93-5.8×10-7Einstein/(Ls)), was examined under simulated solar irradiation. Metal-doped TiO2 samples were prepared reproducibly and doping shifted the optical absorption edge to the visible region. Their activity was superior to the respective of commercially available P25 titania. The reference strains of E. coli and K. pneumoniae proved to be readily inactivated during photocatalytic treatment of aqueous samples, since disinfection occurred rapidly (i.e. after only 10min of irradiation) with the dopant concentration affecting the overall process to a certain extent. Disinfection follows a pseudo-first order kinetic rate in terms of both bacteria removal. Inactivation of the bacteria is attributed to the oxidative degradation of their cells and increase of their cell permeability and not to the potential toxicity of the metal-doped semiconductors, which did not exhibit any bactericidal properties. It has been shown that the improved activity of the Mn-, Co-, and binary Mn/Co doped TiO2 is accredited to the fact that they can be activated in the visible part of the spectrum, in the absence of UV light (i.e. >420nm). © 2014 Elsevier B.V.


PubMed | University of Crete, University of Patras, Institute of Electronic Structure and Laser IESL and Technical University of Crete
Type: | Journal: Journal of environmental management | Year: 2016

The presence of pathogenic microorganisms in wastewater and their resistant nature to antibiotics impose effective disinfection treatment for public health and environmental protection. In this work, photocatalysis with metal-doped titania under artificial and natural sunlight, chlorination and UV-C irradiation were evaluated for their potential to inactivate Klebsiella pneumoniae in real wastewater. Their overall effect on antibiotic resistance profile and target antibiotic resistance genes (ARGs) was also investigated. In particular, Mn-, Co- and binary Mn/Co-TiO


Binas V.D.,Institute of Electronic Structure and Laser IESL | Sambani K.,Institute of Electronic Structure and Laser IESL | Sambani K.,University of Crete | Maggos T.,Greek National Center For Scientific Research | And 3 more authors.
Applied Catalysis B: Environmental | Year: 2012

A straight forward, simple and inexpensive process has been developed by sol-gel method for the synthesis of manganese (Mn) doped and undoped TiO 2 photocatalysts. X-ray powder diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the presence of structural nanoparticles with an average nanocrystalline size of about 20nm. FT-IR/vis adsorption has shown enhanced sub-band-gap absorption as a function of Mn concentration. The photocatalytic activity of these materials was evaluated by the degradation of a basic Methylene Blue (MB) as organic contaminant. Mn-doped TiO 2 powder with molar ratio 0.1:100 was mixed with calcareous filler (5% and 10% respectively) and the photocatalytic activity was evaluated by the degradation of inorganic pollutants such as NO x under UV and visible light. © 2011 Elsevier B.V.


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.


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.


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.


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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