Determination of silver ions in distilled water by stripping voltammetry at a Nafion-coated gold electrode in combination with quartz crystal microbalance and electrochemical impedance spectroscopy

Here, we propose a stripping voltammetric method for Ag+ ion determination in distilled water utilizing screen-printed Au electrodes coated with Nafion (Nafion/Au screen-printed electrodes). The concentration of Ag+ in pure water was determined by linear sweep voltammetry (LSV) after silver deposition on the Nafion/Au electrode. The anodic stripping peak current increased linearly with the concentration of Ag+ ion in the range from 1 ppm to 22 ppm. The LSV oxidative peak current was increased by extending the silver deposition time from 300 s to 500 s. Repetitive LSV measurements revealed satisfactory reproducibility of the Nafion/Au screen-printed electrodes. The detection mechanism was elucidated by recording mass changes of the Nafion/Au electrode with a quartz crystal microbalance (QCM), and by determining changes in the low-frequency capacitance of the Nafion/Au electrode by electrochemical impedance spectroscopy (EIS). The observed changes in mass and capacitance confirmed Ag+ accumulation and release processes at the Nafion/Au electrodes, in good agreement with stripping voltammetry. The combination of stripping voltammetry, QCM and EIS allowed a detailed characterization of the ion transfer, deposition and stripping processes at the Nafion/Au electrodes in presence of Ag+ ions. The Nafion/Au screen-printed electrode enabled voltammetric determination of low Ag+ concentrations in distilled water, without any sample pretreatment nor addition of supporting electrolyte.

SiO2/ZnO Composite Hollow Sub-Micron Fibers: Fabrication from Facile Single Capillary Electrospinning and Their Photoluminescence Properties

In this work, SiO2/ZnO composite hollow sub-micron fibers were fabricated by a facile single capillary electrospinning technique followed by calcination, using tetraethyl orthosilicate (TEOS), polyvinylpyrrolidone (PVP) and ZnO nanoparticles as raw materials. The characterization results of the scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) spectra indicated that the asprepared composite hollow fibers consisted of amorphous SiO2 and hexagonal wurtzite ZnO. The products revealed uniform tubular structure with outer diameters of 400-500 nm and wall thickness of 50-60 nm. The gases generated and the directional escaped mechanism was proposed to illustrate the formation of SiO2/ZnO composite hollow sub-micron fibers. Furthermore, a broad blue emission band was observed in the photoluminescence (PL) of SiO2/ZnO composite hollow sub-micron fibers, exhibiting great potential applications as blue light-emitting candidate materials.

Facile synthesis of three-dimensionally ordered macroporous silicon-doped La0.8K0.2CoO3 perovskite catalysts for soot combustion

Three-dimensionally ordered macroporous (3DOM) silicon-doped La_0.8K_0.2CoO₃ perovskite catalysts were successfully prepared by a colloidal crystal templating method. The catalysts showed a well-ordered macroporous structure and exhibited high activity for soot removal.