Determination of Chromium (VI) in Airborne Particulate Matter by Electrothermal Atomic Absorption Spectrometry

Hexavalent chromium Cr(VI) is a well-established carcinogen associated with lung, nasal, and sinus cancer. Cr(VI) threshold limit values in workroom air have been recently lowered. Consequently, the currently available analytical methods are insufficiently sensitive or high cost. In this paper, a simple, cost-effective, sensitive, and reproducible method using solid-phase extraction with electrothermal atomic absorption spectrometry for determination of hexavalent chromium in airborne samples is reported. The method validation included selectivity, linearity, accuracy, and precision. Interferences from other ions likely to be present in airborne samples, including trivalent chromium, were tested and selectivity was demonstrated. The detection and quantification limits were, respectively, as low as 0.1 and 0.4?µg?L^?1. The linearity ranged from 0.5 to 50.0?µg?L^?1, with a regression coefficients exceeding 0.998. The extraction recovery exceeded 98%. The developed method was successfully compared with a reference spectrophotometric method. The performances achieved were similar to ion chromatography and high-performance liquid chromatography approaches. The novel method was tested on airborne samples collected from the workplace. The method’s performance suggests that it may be an alternative to high-cost techniques for monitoring occupational exposure to hexavalent chromium.     

Enhanced UV photosensing properties of ZnO nanowires prepared by electrodeposition and atomic layer deposition

A new process enabling the synthesis of zinc oxide (ZnO) and Al-doped ZnO nanowires (NWs) for photosensing applications is reported. By combining atomic layer deposition (ALD) for the seed layer preparation and electrodeposition for the NW growth, high-quality ZnO nanomaterials were prepared and tested as ultraviolet (UV) sensors. The obtained NWs are grown as arrays perpendicular to the substrate surface and present diameters between 70 and 130 nm depending on the Al doping, as seen from scanning electron microscopy (SEM) studies. Their hexagonal microstructure has been determined using X-ray diffraction and Raman spectroscopy. An excellent performance in UV sensing has been observed for the ZnO NWs with low Al doping, and a maximal photoresponse current of 11.1 mA has been measured. In addition, initial studies on the stability have shown that the NW photoresponse currents are stable, even after ten UV on/off cycles.     

Enhancing techniques for learning decision trees from imbalanced data

Advances in Data Analysis and Classification - Several machine learning techniques assume that the number of objects in considered classes is approximately similar. Nevertheless, in real-world...     

Photoelectrochemical activity of ZnO:Ag/rGO photo-anodes synthesized by two-steps sol-gel method

This work investigated the influence of silver plasmon and reduced graphene oxide (rGO) on the photoelectrochemical performance (PEC) of ZnO thin films synthesized by the sol-gel method. The physicochemical properties of the obtained photo-anodes were systematically studied by using several characterization techniques. The x-ray diffraction analysis showed that all samples presented hexagonal wurtzite structure with a polycrystalline nature. Raman and energy dispersive x-ray (EDX) studies confirmed the existence of both Ag and rGO in ZnO:Ag/rGO thin films. The estimated grain size obtained from scanning electron microscopy (SEM) analysis decreased with Ag doping, then increased to a maximum value after rGO addition. The UV-vis transmission spectra of the as-prepared ZnO:Ag and ZnO:Ag/rGO thin films have shown a reduction in the visible range with a redshift at the absorption edges. The bandgaps were estimated to be around 3.17 eV, 2.7 eV, and 2.52 eV for ZnO, ZnO:Ag, and ZnO:Ag/rGO, respectively. Moreover, the electrical measurements revealed that the charge exchange processes were enhanced at the ZnO:Ag/rGO/electrolyte interface, accompanied by an increase in the (PEC) performance compared to ZnO and ZnO:Ag photo-anodes. Consequently, the photocurrent density of ZnO:Ag/rGO (0.2 mA·cm^-2) was around 4 and 2.22 times higher than photo-anodes based on undoped ZnO (0.05 mA·cm^-2) and ZnO:Ag (0.09 mA·cm^-2), respectively. Finally, from the flat band potential and donor density, deduced from the Mott-Schottky, it was clear that all the samples were n-type semiconductors with the highest carrier density for the ZnO:Ag/rGO photo-anode.     

Influence of disorder on microcavity polariton linewidths

Polariton linewidths have been measured in a series of microcavities with different excitonic and cavity inhomogeneous broadening in the weak-disorder regime. We show experimentally that the behaviour of the polariton linewidths as a function of the detuning depends on the asymmetric line shape of an inhomogeneously broadened exciton line and particularly the disorder effect can be modulated and cancelled around resonance. When the disorder contribution is minimal, the behaviour of the cavity polariton linewidths tends to one of the homogeneous broadening system.     

Michael addition of 1,3-dicarbonyl compounds catalyzed by iron oxide nanoparticles

Several iron oxides nanoparticles (Fe₂O₃@Fe₂O₃, Fe°@Fe₂O₃, GO@Fe₂O₃ and calcinated Fe₂O₃) have been assessed as catalysts in the 1,4-addition of a cyclic β-ketoester onto methyl vinyl ketone under neat conditions. It appeared that calcinated Fe₂O₃NP are efficient catalysts at 1?mol% loading for the Michael addition of 1,3-dicarbonyl compounds onto various enones.     

Effect of annealing temperatures and of high content of the iron ion (Fe<Superscript>3+</Superscript>)-doping on transition anatase–rutile phase of nanocrystalline TiO<Subscript>2</Subscript> thin films prepared by sol–gel spin coating

Titanium dioxide doped with iron (III) was prepared by sol–gel Spin Coating method. The phase structures, morphologies, particle size of the doped TiO₂ have been characterized by X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectrophotometer. The XRD and Raman results show that the 10% Fe³⁺-doped TiO₂ thin films crystallize in anatase phase between 600 and 800 °C, and into the anatase–rutile phase at 1,000 °C, and further into the rutile phase when the content of Fe³⁺ increases (20%). The grain size calculated from XRD patterns shows that the crystallinity of the obtained anatase particles increased from 39.4 to 43.4 nm as the temperature of annealing increase, whereas the size of rutile crystallites increases, with increasing Fe³⁺ concentrations from 36.9 to 38.1 nm. The AFM surface morphology results confirmed that the particle size increases by increasing the annealing temperature and also with an increasing of Fe³⁺ content. The optical band gap (E _g) of the films was determined by the UV–Vis spectrophotometer. We have found that the optical band gap decreased with an increasing of annealing temperatures and also with an increasing of Fe³⁺ content.     

Solvent free synthesis of 1,3-diaryl-2-propenones catalyzed by commercial acid-clays under ultrasound irradiation

This paper presents a novel solvent free method of synthesis of trans-chalcones. The method was based on ultrasound irradiation of the reagents (aryl methyl ketones and aryl aldehydes) in presence of commercial acid-montmorillonites as catalysts. The trans-chalcones were synthesized in high yields (85–95%) and excellent selectivity in a short reaction time.