Ultrasonic induced photoluminescence decay in sonochemically obtained cauliflower-like ZnO nanostructures with surface 1D nanoarrays

Cauliflower-like ZnO nanostructures with average crystallite size of about 55 nm which have surface one dimensional (1D) nanoarrays with 10 nm diameter were successfully fabricated through a simple sonochemical route. X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and room temperature photoluminescence (PL) characterizations were performed to investigate the morphological and structural properties of the obtained nanostructures. It has been shown that the synthesized cauliflower-like ZnO nanostructures irradiated UV luminescence and a green peak in visible band. Ultrasonic post-treatment of the particles for about 2 h increased the density of surface defects resulted in an increase in the green emission intensity.     

Recent trends in replacement of disperser solvent in dispersive liquid-liquid microextraction methods

Since its innovation in 2006, the dispersive liquid-liquid microextraction (DLLME) method has attracted the attention of analytical chemists in the field of sample preparation. This method has been successfully applied to determine trace amounts of pollutants in various matrices, but the restriction in the choice of suitable disperser and extraction solvents, and high disperser solvent consumption leading to decreased partition coefficients of the analytes between aqueous phase and extractant are its problems. To solve these drawbacks and develop environmentally friendly techniques, various alternatives for the conventional DLLME have been presented. The current review will begin with an introduction to the sample preparation, implementation of DLLME, and its advantages. Then, we focus on its drawbacks, which result mainly from the use of disperser solvent. Afterward, some of the most interesting approaches that have been employed and published until now are reviewed. Finally, an outlook on the future of these techniques will be given.     

Supercritical fluid extraction followed by supramolecular solvent microextraction as a fast and efficient preconcentration method for determination of polycyclic aromatic hydrocarbons in apple peels

In this work, reverse micelle‐based supramolecular solvent microextraction method coupled with supercritical fluid extraction and used for determining trace amounts of polycyclic aromatic hydrocarbons in apple peels. The extract was analyzed by high‐performance liquid chromatography equipped with a fluorescence detector. Coupling supramolecular solvent microextraction with supercritical fluid extraction method, resolve low preconcentration factor of supercritical fluid extraction method, improved limit of detection of polycyclic aromatic hydrocarbons and allow the use of supramolecular solvent microextraction in solid matrices. The effective parameters on the supramolecular solvent microextraction and supercritical fluid extraction efficiency were optimized using one variable at a time and face centered design methods, respectively. Under the optimum condition, the limits of detection and limits of quantifications were in the range of 0.34–1.27 and 1.03–3.82 µg/kg, respectively. Analysis of polycyclic aromatic hydrocarbons in apple peels showed that the supercritical fluid extraction/ supramolecular solvent microextraction method provide great potential for trace analysis of polycyclic aromatic hydrocarbons in fruit samples (RSDs < 7.7%).     

Photocatalytic activities of multilayered ZnO-based thin films prepared by sol–gel route: effect of SnO2 heterojunction layer

In present study, ZnO/SnO₂/ZnO/SnO₂/ZnO multi–layer, ZnO/SnO₂/ZnO triple layer and ZnO single layer films have been deposited on glass substrate by sol–gel dip–coating technique. The structural and optical properties of thin films have been investigated by X-ray diffractometer, UV–visible, photoluminescence spectroscopies and scanning electron microscopy. The structural analysis reveals structural inhomogeneities and different crystallite growth processes as function of number of deposited layers. A comparison between photocatalytic activity of zinc oxide samples toward photodegradation of phenol, 4-aminophenol and 4-nitrophenol has been performed under UV light irradiation. Experiments were conducted to study the effects of operational parameters on the degradation rate. Pseudo-first-order photodegradation kinetics was observed on all films and the reaction constants were determined. The results showed that the photocatalytic activity of ZnO multi–layer film was superior to that of the ZnO single- and triple-layer films. Differences in film efficiencies can be attributed to differences in crystallinity, surface morphology, defect concentration of oxygen vacancy and to presence of SnO₂ sublayer that may act as trap for electrons generated in the ZnO layer thus preventing electron–hole recombination. The results reveal that SnO₂ hetrojunction layers improve crystalline quality, optical and photocatalytic properties of ZnO multilayered films.     

Effect of sputtering pressure on structural and optical properties of silver oxide thin films; Kramers–Kronig method

Silver oxide nano layers were prepared by RF magnetron sputtering on amorphous SiO₂ substrates. O₂ pressure in chamber was varied from 1 to 4 and 7 mTorr during growth process. The effects of different O₂ pressure on structural, morphological and optical properties of the films were investigated by means of X-ray diffraction, scanning electron microscopy, atomic force microscopy and UV–Vis spectroscopy analyses. Optical reflectance measured in the wavelength of 350–950 nm by spectroscopy. Other optical properties and optical band gaps were calculated using Kramers–Kronig relations. The X-ray diffraction measurements showed change in crystalline structure with increasing O₂ pressure. Preferred orientation has been changed to another growth orientation at 4 mTorr O₂ pressure. The Atomic force microscope images showed increasing in roughness consistently by increasing oxygen pressure. The thickness of the thin films decreases (from 217 to 180 nm) with increasing O₂ pressure. Optical results revealed that the highest optical band gap of 3.1 eV and the highest transmittance of?~?80% were achieved at lower O₂ pressure (1 mTorr).