Modified nanoalumina sorbent for sensitive trace cobalt determination in environmental and food samples by flame atomic absorption spectrometry

1-(2-pryidylazo)-2-naphthol (PAN) immobilized on sodium dodecyl sulfate-coated nano alumina was developed for the preconcentration and determination of metal cations Co (II) from environmental and food samples. The research results displayed that adsorbent has the highest adsorption capacity for Co (II) in this system. Desorption by elution of the adsorbent with 2.0?ml of a mixture of nitric acid and ethanol was carried out. After phase separation, the enriched analyte in the final solution is determined by flame atomic absorption spectrometry (FAAS) by using a micro sample introduction system. Analytical influencing parameters including pH value, amount of sorbent, equilibrium time, sample volume, volume and concentration of eluent were examined. The effect of common matrix ions has also been investigated and it was found that they had no influence on cobalt preconcentration. Under the optimum experimental conditions, the maximum capacity of sorbent was obtained as 20?mg?g^?1. The preconcentration factor and limit of detection were found to be 250 and 0.15?µg?L^?1, respectively. This method showed good precision with the relative standard deviation (RSD) of 2.4% and 2.1% in concentrations of 20 and 50?µg?L^?1, respectively. The accuracy of the method was evaluated by comparison of results with those obtained by electrothermal atomic absorption spectrometry. This method was successfully applied for preconcentration and determination of Co (II) in environmental and food samples.     

Anodizing parameters optimization of Ti–6Al–4V titanium alloy using response surface methodology

The present paper depicts application of response surface methodology (RSM) for optimizing the anodizing parameters of Ti–6Al–4V (TA6V) titanium alloy. Three operating parameters, i.e., voltage (V), temperature (T) and time (t), are designed as factors by using RSM design. Reliable regression models were established between the input parameters and the given responses, namely oxide thickness (e), Vickers hardness (Hv) and polarization resistance (R_p) with regression coefficients multiples of 0.940, 0.925, 0.865, respectively, indicating good agreement between the experimental values and those predicted using the quadratic model.The predicted values of V (42.67 V), t (45.9 min) and T (29.5 °C) are the optimal anodization combination leading to a TiO₂ layer with the best compromise between the oxide thickness (28.7 μm), Vickers hardness (321.90) and bias resistance (6.37 MΩ cm²). It was observed that the hardness characteristic is more affected by anodizing time and temperature, and less sensitive to voltage and parameter interactions. Polarization resistance is strongly influenced by voltage, modestly influenced by anodizing time and temperature, and less sensitive to parameter interactions. Moreover, higher anodizing parameters lead to higher thickness. Therefore, RMS could be a suitable method to optimize anodizing parameters of titanium alloys.     

Formation of well-packed TiO<Subscript>2</Subscript> nanoparticles on multiwall carbon nanotubes using CVD method to fabricate high sensitive gas sensors

Titanium oxide nanoparticles were coated on multiwall carbon nanotubes (MWCNTs) using an atmospheric pressure chemical vapor deposition (CVD) to achieve highly compact nanoparticles of about 5 nm on CNT structure. The CNTs with a diameter of about 50 nm were grown by plasma enhanced CVD. Gas sensitivity of the fabricated structure was investigated and compared with TiO₂/CNT composite-based gas sensors. The effect of the structural interaction between the nanoparticles and the CNT wall on sensing mechanism of the as-prepared gas sensors was investigated. Ultrasensitive gas sensors were obtained by TiO₂/CNT nanostructures with strong interaction between the MWCNT and the TiO₂ nanoparticles. The measurements show high chemical activity and exceptional electrical response of the as-prepared structure being exposed to gases. Scanning and transmission electron microscopy and X-ray diffraction analysis were used to obtain structural information.