G. Vourlias

Kilogram-scale synthesis of iron oxy-hydroxides with improved arsenic removal capacity: Study of Fe(II) oxidation–precipitation parameters

Various iron oxy-hydroxides were synthesized in a continuous flow kilogram-scale production reactor through the precipitation of FeSO(4) and FeCl(2) in the pH range 3-12 under intense oxidative conditions to serve as arsenic adsorbents. The selection of the optimum adsorbent and the corresponding conditions of the synthesis was based not only on its maximum As(III) and As(V) adsorption capacity but also on its potential efficiency to achieve the arsenic health regulation limit in NSF challenge water. As a result, the adsorbent prepared at pH 4, which consists of schwertmannite, was selected because it exhibited the highest adsorption capacity of 13 μg As(V)/mg, while maintaining a residual arsenic concentration of 10 μg/L at an equilibrium pH 7. The high surface charge and the activation of an ion-exchange mechanism between SO(4)(2-) adsorbed in the Stern layer and arsenate ions were found to significantly contribute to the increased adsorption capacity. Adsorption capacity values observed in rapid scale column experiments illustrate the improved efficiency of the qualified adsorbent compared to the common commercial arsenic adsorbents.

Tetravalent manganese feroxyhyte: a novel nanoadsorbent equally selective for As(III) and As(V) removal from drinking water.

The development of a single-phase Fe/Mn oxy-hydroxide (δ-Fe0.76Mn0.24OOH), highly efficient at adsorbing both As(III) and As(V), is reported. Its synthesis involves the coprecipitation of FeSO4 and KMnO4 in a kilogram-scale continuous process, in acidic and strongly oxidizing environments. The produced material was identified as a manganese feroxyhyte in which tetravalent manganese is homogeneously distributed into the crystal unit, whereas a second-order hollow spherical morphology is favored. According to this structuration, the oxy-hydroxide maintains the high adsorption capacity for As(V) of a single Fe oxy-hydroxide combined with enhanced As(III) removal based on the oxidizing mediation of Mn(IV). Ion-exchange between arsenic species and sulfates as well as the strongly positive surface charge further facilitate arsenic adsorption. Batch adsorption tests performed in natural-like water indicate that Mn(IV)-feroxyhyte can remove 11.7 μg As(V)/mg and 6.7 μg As(III)/mg at equilibrium pH 7, before residual concentration overcomes the regulation limit of 10 μg As/L for drinking water. The improved efficiency of this material, its low cost, and the possibility for scaling-up its production to industry indicate the high practical impact and environmental importance of this novel adsorbent.

Small Molecule/Polymer Blend Organic Transistors with Hole Mobility Exceeding 13 cm V−1 s−1

A ternary organic semiconducting blend composed of a small-molecule, a conjugated polymer, and a molecular p-dopant is developed and used in solution-processed organic transistors with hole mobility exceeding 13 cm(2) V(-1) s(-1) (see the Figure). It is shown that key to this development is the incorporation of the p-dopant and the formation of a vertically phase-separated film microstructure.

Incineration of tannery sludge under oxic and anoxic conditions: study of chromium speciation.

A tannery sludge, produced from physico-chemical treatment of tannery wastewaters, was incinerated without any pre-treatment process under oxic and anoxic conditions, by controlling the abundance of oxygen. Incineration in oxic conditions was performed at the temperature range from 300°C to 1200°C for duration of 2h, while in anoxic conditions at the temperature range from 400°C to 600°C and varying durations. Incineration under oxic conditions at 500°C resulted in almost total oxidation of Cr(III) to Cr(VI), with CaCrO4 to be the crystalline phase containing Cr(VI). At higher temperatures a part of Cr(VI) was reduced, mainly due to the formation of MgCr2O4. At 1200°C approximately 30% of Cr(VI) was reduced to Cr(III). Incineration under anoxic conditions substantially reduced the extent of oxidation of Cr(III) to Cr(VI). Increase of temperature and duration of incineration lead to increase of Cr(VI) content, while no chromium containing crystalline phase was detected.

Efficient organic solar cells using copper(I) iodide (CuI) hole transport layers

We report the fabrication of high power conversion efficiency (PCE) polymer/fullerene bulk heterojunction (BHJ) photovoltaic cells using solution-processed Copper (I) Iodide (CuI) as hole transport layer (HTL). Our devices exhibit a PCE value of ∼5.5% which is equivalent to that obtained for control devices based on the commonly used conductive polymer poly(3,4-ethylenedioxythiophene): polystyrenesulfonate as HTL. Inverted cells with PCEu2009>3% were also demonstrated using solution-processed metal oxide electron transport layers, with a CuI HTL evaporated on top of the BHJ. The high optical transparency and suitable energetics of CuI make it attractive for application in a range of inexpensive large-area optoelectronic devices.

Cu-Zn powders as potential Cr(VI) adsorbents for drinking water

This work examines the possibility of applying CuZn alloys as a reducing medium for the efficient removal of hexavalent chromium from drinking water. In an effort to develop a route for producing powders of CuZn alloys under mild conditions and investigate the optimum composition for such application, a series of alloys in the form of powders were prepared, by a sequence of Cu and Zn ball-milling and low temperature annealing. Batch Cr(VI) removal tests, performed to evaluate and compare the efficiency of the products under typical natural water parameters (pH 7 and natural-like water), indicated that the best performing material have a composition around 50 wt% Cu. The dominant reduction mechanisms are both the corrosion of the alloy surface and the electron transfer to the solution. The behavior of granulated CuZn media was tested in rapid-scale column tests using the commercial KDF which verified the high potential of CuZn alloys in Cr(VI) removal. Nevertheless, Cu and Zn leaching problems should be also considered.

Solution processed SnO2:Sb transparent conductive oxide as an alternative to indium tin oxide for applications in organic light emitting diodes

Here, we present the deposition of antimony-doped tin oxide thin films using the ambient spray pyrolysis technique and demonstrate their implementation as transparent electrodes (anodes) in red, green and blue organic light emitting diodes. The films were spray coated at 380 °C from SnCl4 and SbCl3 solution blends in methanol and ∼230 nm thick films were investigated by means of X-ray diffraction, AFM, UV-Vis absorption spectroscopy, 4-point probe, Hall effect measurements and Kelvin probe. It was found that for optimum antimony doping in the precursor solution of ∼2 wt%, the as-deposited ATO films exhibit excellent characteristics such as a low surface roughness (RRMS) of ∼ 6.3 nm, a high work function (∼−5.03 eV), a wide direct band gap (∼4.2 eV), high transparency in the visible spectrum in excess of 85% on glass, a low sheet resistivity (∼32 Ohms sq−1), a high charge carrier concentration (∼6.35 × 1020 cm−3) and a carrier mobility of ∼32 cm2 V−1 s−1. Furthermore, the electrical and optical performance i.e. the turn on voltage and external quantum efficiency of red, green and blue OLEDs fabricated on optimized SnO2:Sb films were identical to those of OLEDs fabricated on commercially available ITO (Rs ∼ 15 Ohms sq−1) and were found to be in excess of 11%, 0.3% and 13% for red, green and blue OLEDs, respectively.

Understanding the mechanical and thermal property reinforcement of crosslinked polyethylene by nanodiamonds and carbon nanotubes

A comprehensive investigation of the mechanical and thermal property reinforcement of silane-crosslinked polyethylene nanocomposites, containing small amounts of multi-walled carbon nanotubes (MWCNTs) and nanodiamonds (NDs), is presented in this work. Lower filler concentrations allowed a satisfactory dispersion, enabling the successful reinforcement of the matrix in every aspect. As the nanofiller content increased, the formed aggregates enlarged and the performance of the composites became more brittle. The measured stiffness enhancement of all the composites was found to be mainly influenced by the crystalline characteristics of the matrix and filler–matrix adhesion. Moreover, it was concluded that filler dispersion and filler–matrix interactions govern the ultimate strength and toughness behavior of these composites, which were found to slightly increase in minimum filler concentrations. Fractography was employed to study the embrittleness of the composites with higher filler loadings, and the observations revealed that a ductile to brittle transition is caused by a micro-deformation mechanism change in these composites. Furthermore, the prepared composites had a significantly improved thermal conductivity, which was mainly related to their superior specific heat capacity, while a great thermal stability enhancement was also revealed.

Thermal conductivity and degradation behavior of HDPE/graphene nanocomposites

Graphene-filled high-density polyethylene nanocomposites varying filler’s size (5, 10 and 25xa0×xa010−6 m in diameter) were prepared by the melt-mixing method, and their thermal properties are then investigated by TG, Py–GC/MS and thermal conductivity measurements. Thermal and thermo-oxidative degradation temperatures of HDPE/graphene nanocomposites were substantially improved with increment of filler content and graphene size. According to kinetic analysis of thermal decomposition, the thermal degradation mechanism of HDPE/graphene nanocomposites may efficiently be described by an nth-order model with autocatalysis (Cn). Meanwhile, the activation energy values versus the partial mass loss revealed that graphene nanoparticles take up the heat and obstruct transport of HDPE degradation products efficiently. It was also found that the decomposition in nanocomposites is taking place mainly via chain scission reaction, followed by β-scission propagation reactions, radical reactions and the termination process. Graphene nanocomposites achieved significant improvements in thermal conductivity at low filler concentrations, while the experimental data are in good agreement with the Hatta–Taya theoretical model. Summing up the influence of filler size on thermal properties of polymer matrix, graphene nanoparticles with the higher diameter (25xa0×xa010−6xa0m) affect more than graphene of 5xa0×xa010−6 and 15xa0×xa010−6xa0m.

Remarkable Enhancement of the Hole Mobility in Several Organic Small‐Molecules, Polymers, and Small‐Molecule:Polymer Blend Transistors by Simple Admixing of the Lewis Acid p‐Dopant B(C6F5)3

Abstract Improving the charge carrier mobility of solution‐processable organic semiconductors is critical for the development of advanced organic thin‐film transistors and their application in the emerging sector of printed electronics. Here, a simple method is reported for enhancing the hole mobility in a wide range of organic semiconductors, including small‐molecules, polymers, and small‐molecule:polymer blends, with the latter systems exhibiting the highest mobility. The method is simple and relies on admixing of the molecular Lewis acid B(C6F5)3 in the semiconductor formulation prior to solution deposition. Two prototypical semiconductors where B(C6F5)3 is shown to have a remarkable impact are the blends of 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene:poly(triarylamine) (diF‐TESADT:PTAA) and 2,7‐dioctyl[1]‐benzothieno[3,2‐b][1]benzothiophene:poly(indacenodithiophene‐co‐benzothiadiazole) (C8‐BTBT:C16‐IDTBT), for which hole mobilities of 8 and 11 cm2 V−1 s−1, respectively, are obtained. Doping of the 6,13‐bis(triisopropylsilylethynyl)pentacene:PTAA blend with B(C6F5)3 is also shown to increase the maximum hole mobility to 3.7 cm2 V−1 s−1. Analysis of the single and multicomponent materials reveals that B(C6F5)3 plays a dual role, first acting as an efficient p‐dopant, and secondly as a microstructure modifier. Semiconductors that undergo simultaneous p‐doping and dopant‐induced long‐range crystallization are found to consistently outperform transistors based on the pristine materials. Our work underscores Lewis acid doping as a generic strategy towards high performance printed organic microelectronics.