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Monitoring of pesticide residues in food, beverages, and the environment requires fast, versatile, and sensitive analyzing methods. Direct electrochemical detection of pesticides could represent an efficient solution. Adequate electrode material, electrochemical technique, and optimal operation parameters define the detection method for practical application. In this study, cyclic voltammetric and differential pulse voltammetric techniques were used in order to individually and simultaneously detect two pesticides, i.e., carbaryl (CR) and paraquat (PQ), from an acetate buffer solution and also from natural apple juice. A graphene-modified boron-doped diamond electrode, denoted BDDGR, was obtained and successfully applied in the simultaneous detection of CR and PQ pesticides, using the differential pulse voltammetric technique with remarkable electroanalytical parameters in terms of sensitivity: 33.27 μA μM−1 cm−2 for CR and 31.83 μA μM−1 cm−2 for PQ. These outstanding results obtained in the acetate buffer supporting electrolyte allowed us to simultaneously detect the targeted pesticides in natural apple juice., ChemE/Materials for Energy Conversion & Storage

Three types of composite electrode materials, i.e. carbon nanotubes-epoxy (CNT), zeolite-carbon nanotubes-epoxy (ZCNT) and TiO2-modified zeolite-carbon nanotubes-epoxy (TiZCNT), were synthesized, morphologically and electrically characterized, and tested in the photoelectrodegradation of pentachlorophenol (PCP) from water. The electrode composite materials were synthesized by the two-roll mill method, and a higher porosity of zeolite-modified electrode, caused by the zeolite incorporation, was noticed by means of scanning electron microscopy. Electroactive surface area, determined by classical methods using cyclic voltammetry (CV), and electric conductivity, determined by the four-point method, were negatively affected by the presence of zeolite. The photoelectrochemical behaviour of the electrodes, under ultraviolet (UV) irradiation, towards the pentachlorophenol oxidation was studied, and the photoelectrocatalytic activity of each electrode was determined. The PCP oxidation occurred in two steps at +0.65 V and +0.94 V vs. saturated calomel electrode SCE under UV irradiation. The oxidation peak recorded at +0.65 V vs. SCE appeared only under UV irradiation and it is considered that the photoelectrooxidation peak corresponded to PCP photoelectrooxidation. Also, the enhancement of PCP electrooxidation at +0.94 V vs. SCE was noticed under UV irradiation, which confirmed the photelectrocatalytic activity. The performance of the PCP degradation process, expressed as degradation efficiency and electrochemical efficiency, recommended the operation of photoelectrocatalysis at a bias voltage application of +0.8 V/SCE, while the mineralization degree recommended a bias voltage value of +1.5 V/SCE., ChemE/Materials for Energy Conversion & Storage

The electrochemical methods-based protocol for simultaneous detection of tetracycline (TC) from antibiotics class and fluoxetine (FXT) from anti-depressive pharmaceuticals class, which belongs to emerging pollutants from water, was developed in this study using carbon nanofiber-epoxy composite electrode (CNF). The electrochemical behaviour of each pharmaceutical on CNF was considered the basis for simultaneous detection of both pharmaceuticals from water. TC electrooxidation on CNF occurred in two steps and, consequently, two detection potentials are considered. FXT electrooxidation occurred in one step that is overlaid to the first step of TC detection, this step being considered as cumulative for both pharmaceuticals. Each electrochemical method of cyclic voltammetry (CV) and differential-pulsed voltammetry (DPV) allowed detecting cumulative presence of TC and FXT at the detection potential ranged between 0.65 and 0.815 V vs. SCE and the selective detection of TC at the detection potential ranged between 0.956 and 1.14 V vs. SCE. The electroanalytical parameters related to the lowest limit of detection and sensitivity recommended this electrode to exhibit the potential for practical applications in the electrochemical detection of certain pharmaceuticals as emerging pollutants from water., ChemE/Materials for Energy Conversion & Storage

In this study, the detection protocols for the individual, selective, and simultaneous determination of ibuprofen (IBP) and diclofenac (DCF) in aqueous solutions have been developed using HKUST-1 metal-organic framework-carbon nanofiber composite (HKUST-CNF) electrode. The morphological and electrical characterization of modified composite electrode prepared by film casting was studied by scanning electronic microscopy and four-point-probe methods. The electrochemical characterization of the electrode by cyclic voltammetry (CV) was considered the reference basis for the optimization of the operating conditions for chronoamperometry (CA) and multiple-pulsed amperometry (MPA). This electrode exhibited the possibility to selectively detect IBP and DCF by simple switching the detection potential using CA. However, the MPA operated under optimum working conditions of four potential levels selected based on CV shape in relation to the potential value, pulse time, and potential level number, and order allowed the selective/simultaneous detection of IBP and DCF characterized by the enhanced detection performance. For this application, the HKUST-CNF electrode exhibited a good stability and reproducibility of the results was achieved., ChemE/Catalysis Engineering, ChemE/Materials for Energy Conversion & Storage

Places of large potentials of sustainable energy production and places of energy consumption are often very different and separated by large distances across the globe. This paper first discusses potentials of solar technology in terms of global availability using PV technology and actual energy production. Solar energy is widely under-used and one way to reduce this is to improve production in low-energy places with high demand: large cities. According to this option, about 40% of the electricity consumption in the built environment could be produced by solar PV systems. To reach this goal appropriate solar PV energy conversion devices and energy storage systems are needed. This paper discusses conditions in the built environment and functional and design qualities enabling an increased diffusion of the technologies. In a comparative analysis of PV technologies, the criteria taken into account encompass efficiency of the type of solar cell and commercial availability. Special attention is paid to the design features of different PV systems, like flexibility, colour and transparency that might help in their utilization as integrated in building material and ornaments in modern architecture. The same procedure is followed for electricity storage devices. The preliminary conclusion is that at present the freedom of design is largest for a combination of crystalline silicon PV cells and Li-ion batteries. Implications for urban policy will be discussed., Innovation Systems, Technology, Policy and Management

The aim of this study was the preparation, characterization, and application of a multi-wall carbon nanotubes-epoxy composite electrode (MWCNT-EP) with 25%, wt. MWCNTs loading for the voltammetric/amperometric determination of pentachlorophenol (PCP) in aqueous solutions. The structural and morphological aspects of the MWCNT-EP composite electrode were examined by scanning electron microscopy. The electrical properties were characterized by direct-current conductivity measurements in relation with the percolation threshold. The electrochemical behavior of PCP at the MWCNT-EP composite electrode was investigated using cyclic voltammetry in 0.1 M Na2SO4 supporting electrolyte in order to establish the parameters for amperometric/voltammetric determination of PCP. The linear dependence of current vs. PCP concentrations was reached in a wide concentration range from 0.2 to 12 ?M PCP using cyclic voltammetry, differential-pulsed voltammetry, square-wave voltammetry, chronoamperometry, and multiple-pulsed amperometry techniques. The best electroanalytical performances of this composite electrode were achieved using a pre-concentration/square-wave voltammetric technique and also multiple-pulsed amperometry techniques envisaging the practical applications. The ease of preparation, high sensitivity, and stability of this composite electrode should open novel avenues and applications for fabricating robust sensors for detection of many important species., ChemE/Chemical Engineering, Applied Sciences

The aim of this study is to prepare and characterize two types of silver-functionalized carbon nanofiber (CNF) composite electrodes, i.e., silver-decorated CNF-epoxy and silver-modified natural zeolite-CNF-epoxy composite electrodes suitable for ibuprofen detection in aqueous solution. Ag carbon nanotube composite electrode exhibited the best electroanalytical parameters through applying preconcentration/differential-pulsed voltammetry scheme., Chemical Engineering, Applied Sciences

The aim of this study was to prepare three types of multiwall carbon nanotubes (CNT)-based composite electrodes and to modify their surface by copper electrodeposition for nonenzymatic oxidation and determination of glucose from aqueous solution. Copper-decorated multiwall carbon nanotubes composite electrode (Cu/CNT-epoxy) exhibited the highest sensitivity to glucose determination., Chemical Engineering, Applied Sciences

RU Radboud Universiteit Nijmegen, 29 januari 2010, Promotores : Jansen, J.A., Schoonman, J. Co-promotores : Wolke, J.G.C., Leeuwenburgh, S.C.G., Contains fulltext : 88724.pdf (Publisher’s version ) (Open Access)

Bulk BaxSr1 - xCoyFe1 - yO3 - dBaxSr1?xCoyFe1?yO3? compositions (BSCF) were synthesized by the solid-state reaction method. The electrical conductivity of ceramic bars was measured using a dc four-probe method as a function of temperature in air up to 970 °C. All compositions showed thermally activated p-type semi-conductivity up to ~450 °C and then a transition to metal-like conductivity. The small-polaron hopping p-type semi-conductivity depends on the oxygen nonstoichiometry, which increases with increasing temperature. Metal-like conductivity is attributed to the overlap of the transition metal d-electron orbitals with the oxygen p-orbitals. Strontium-rich compositions show higher conductivity. The Co/Fe ratio does not influence much the p-type semi-conduction. Iron-rich compositions revealed more metal-like conduction behavior. The degree of overlap between transition metal d-orbitals and oxygen p-orbitals depends on the Ba/Sr as well as on the Co/Fe ratios., Chemical Engineering, Applied Sciences

Process and Energy, Mechanical, Maritime and Materials Engineering

Semiconductor metal oxide films of copper-doped tin oxide (Cu-SnO2), tungsten oxide (WO3) and indium oxide (In2O3) were deposited on a platinum coated alumina substrate employing the electrostatic spray deposition technique (ESD). The morphology studied with scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows porous homogeneous films comprising uniformly distributed aggregates of nano particles. The X-ray diffraction technique (XRD) proves the formation of crystalline phases with no impurities. Besides, the Raman cartographies provided information about the structural homogeneity. Some of the films are highly sensitive to low concentrations of H2S (10 ppm) at low operating temperatures (100 and 200 °C) and the best response in terms of Rair/Rgas is given by Cu-SnO2 films (2500) followed by WO3 (1200) and In2O3 (75). Moreover, all the films exhibit no cross-sensitivity to other reducing (SO2) or oxidizing (NO2) gases., ChemE/Chemical Engineering, Applied Sciences

Electrochemical impedance measurements were carried out on symmetrical nickel/gadolinia-doped ceria test cells. For H2, N2, and H2O mixtures, the diffusion length obtained based on the impedance measurements is on the order of centimeters. This high value of the diffusion length is attributed to the flow field in the reactor. It is suggested that a detailed analysis of the gas flow field inside the test reactor is essential before interpreting the impedance measurements with various solid oxide fuel cell test configurations., Process and Energy, Mechanical, Maritime and Materials Engineering

Time-of-Flight (TOF) measurements have been performed on n-type TiO2/p-type CuInS2 heterojunctions. The TiO2 film thickness has been varied between 200 and 400 nm, while the CuInS2 film thickness has been fixed at 500 nm. The TOF response can be accurately modeled, if the potential drop across the p-n heterojunction with a large density of interface states is properly accounted for. Also electron transport in a space-charge region for a not fully depleted semiconductor has to be considered. The electron mobility in TiO2 is found to be 10?2?cm2?V?1?s?1, independent of the TiO2 layer thickness. The interface-state densities are 5×1011, 2×1012, and 6×1012?eV?1?cm?2 for 200, 300, and 400 nm thick TiO2 films, respectively., Applied Sciences

In this paper, a modified expanded graphite composite electrode based on natural zeolitic volcanic tuff modified with silver (EG-Ag-Z-Epoxy) was developed. Cyclic voltammetry measurements revealed a reasonably fast electron transfer and a good stability of the electrode in 0.1 M NaOH supporting electrolyte. This modified electrode exhibited moderate electrocatalytic effect towards urea oxidation, allowing its determination in aqueous solution. The linear dependence of the current versus urea concentration was reached using square-wave voltammetry in the concentrations range of urea between 0.2 to 1.4 mM, with a relatively low limit of detection of 0.05 mM. A moderate enhancement of electroanalytical sensitivity for the determination of urea at EG-Ag-Z-Epoxy electrode was reached by applying a chemical preconcentration step prior to voltammetric/amperometric quantification., ChemE/Chemical Engineering, Applied Sciences

Photoinduced interfacial charge carrier generation, separation, trapping, and recombination in TiO2?In2S3?CuInS2 cells have been studied with time-resolved microwave conductivity (TRMC). Single layer, double layer, and complete triple layer configurations have been studied. Selective electronic excitation in one of the components is accomplished by using monochromatic pulsed laser excitation. In bare CuInS2 films and in TiO2?CuInS2 double layers, photoinduced charge carriers recombine on a subnanosecond time scale. This fast recombination slows down significantly when an In2S3 buffer layer is applied between TiO2 and CuInS2. In that case, the charge separation lifetime increases by more than one order of magnitude. A superlinear dependence of the TRMC signals on the incident laser intensity is observed for the triple layer configuration, which indicates saturation of electron traps in In2S3 or hole traps in CuInS2. Furthermore, TRMC signals from TiO2?In2S3?CuInS2 triple junctions and those from In2S3?CuInS2 double layers are identical, which shows that charge carrier separation exclusively takes place at the In2S3?CuInS2 interface., DelftChemTech, Applied Sciences