Low-cost nanostructured Fe2O3-based composite catalysts synthesized by mechanical milling for CO oxidation reaction

In this work, the catalytic properties of low-cost nanostructured iron oxide have been improved by the mechanical milling method through combination with copper and cobalt oxide. Synthesized catalysts were characterized by X-ray diffraction, transition electron microscopy, and Brunauer–Emmet–Teller techniques. Also, the catalytic activity and stability of the powders for CO oxidation reaction were investigated. Results indicated that the catalytic activity of the powders has significantly improved after mechanical milling. Minimum complete conversion temperatures for Co–Fe and Cu–Fe composite oxide catalysts were around 245 and 275°C, respectively. No decline in the activity of the catalysts was observed during the long-term stability test. Furthermore, catalytic activity of the composite powders, especially Co–Fe improves at subsequent cycles. In general, cycle durability, stability at high temperature and reaction rate of the iron oxide powder has been improved using it as Cu–Fe and Co–Fe oxide composites.     

Highly Selective Cyanide Coated-Wire Electrode Based on a Recently Synthesized Co(II) Complex With the N,N′ -Bis(2-Quinolinecarboxamido)- 1,2-Benzene Applying Batch and Flow Injection Analysis Techniques

A poly(vinyl chloride) (PVC)-based coated wire electrode based on [Co(II)bqb] (bqb = N,N'-bis(2-quinolinecarboxamido)-1,2-benzene) as a novel sensing material for determination of trace amounts of cyanide ions is successfully developed. The effect of electrode substrate, membrane composition and pH of the working solution on the behavior of the sensor was investigated. The electrode was also used in flow injection potentiometry by a home-made flow cell. The electrode revealed Nernstian response towards cyanide anion over the concentration ranges 3.2times10^-7 to 2.0times10^-4 molldrL^-1 and 5.0times10^-6 to 1.0times10^-3 molldrL^-1 applying batch and flow injection analysis (FIA), respectively. The lower detection limits are 3.2times10^-7 molldrL^-1 and 5.0times10^-6 molldrL^-1 for batch and FIA, respectively. The electrode shows a short response time (<5 s) in the whole concentration range. The selectivity of the electrode in comparison with most of cyanide selective electrodes is high. The flow cell is simple to construct and free from memory effect problems over long periods of use. The proposed electrode was successfully applied for the determination of cyanide in commercially available spring water under both batch and flow injection conditions. A comparative study revealed no significant difference between ASTM method and the proposed technique.     

Absolute measurements of radiation damage in nanometer-thick films

The problem of absolute measurements of radiation damage in films of nanometer thicknesses is addressed. Thin films of DNA (～2-160 nm) are deposited onto glass substrates and irradiated with varying doses of 1.5-keV X-rays under dry N(2) at atmospheric pressure and room temperature. For each different thickness, the damage is assessed by measuring the loss of the supercoiled configuration as a function of incident photon fluence. From the exposure curves, the G-values are deduced, assuming that X-ray photons interacting with DNA deposit all of their energy in the film. The results show that the G-value (i.e. damage per unit of deposited energy) increases with film thickness and reaches a plateau at 30±5 nm. This thickness dependence provides a correction factor to estimate the actual G-value for films with thicknesses <30 nm thickness. Thus, the absolute values of the damage can be compared with that of films of any thickness under different experimental conditions.     

Comparison of different methodologies for integration of molecularly imprinted polymer and electrochemical transducer in order to develop a paraoxon voltammetric sensor

In this work a paraoxon voltammetric sensor was introduced. Different methods for integration of molecularly imprinted polymer (MIP) and electrochemical transducer were investigated. Three techniques including MIP particles embedding in the carbon paste (CP) (MIP-CP), coupling of MIP with the glassy carbon electrode (GC) surface by using poly epychloro hydrine (PECH) (MIP/PECH-GC) and MIP/graphite mixture thin layer attachment onto the glassy carbon electrode (MIP/Graphite-PECH-GC) were tested. The prepared electrodes were applied for paraoxon measurement by using a three-step procedure including analyte extraction in the electrode, electrode washing and electrochemical measurement of paraoxon. The washing of electrodes, after paraoxon extraction, led to high selectivity of electrode for paraoxon. It was found that MIP-CP electrode had higher response to paraoxon in comparison to other tested electrodes. Besides, the washing process decreased response magnitude of MIP/PECH-GC and MIP/Graphite-PECH-GC but, the response of MIP-CP was not affected considerably by the washing. Parathion was chosen to evaluate the selectivity of MIP based sensors. It was proved that the MIP-CP had better selectivity, wider linear range and lower detection limit in comparison to other tested electrodes. The developed MIP-CP electrode was used as a high selective sensor for paraoxon determination in water and vegetable samples.     

Mechanical properties of calcium silicate hydrates

The dynamic mechanical properties of compacted samples of synthetic calcium silicate hydrate (C–S–H) were determined at variable stoichiometries (C/S ratio). The stiffness and damping properties of the C–S–H systems were monitored at various increments of mass loss from 11%RH following the removal of the adsorbed and interlayer water. The changes in the storage modulus (E′) and internal friction (tan δ) were discussed in terms of the state of water present in the nanostructure of C–S–H, the evolution of the silicate structure and the interaction of calcium ions in the interlayer region. Results were compared to those for the hydrated Portland cement paste and porous glass. It was shown that the C–S–H in the hydrated Portland cement has a complex yet analogous dynamic mechanical behavior to that of the synthetic C–S–H. The response of these systems upon the removal of water was explained by a layered model for the C–S–H. A mechanistic model was proposed to describe the changes occurring at various stages in the dynamic mechanical response of C–S–H.     

Sol–gel synthesis of silicon carbide on silicon pyramids: a promising candidate for supercapacitor electrodes

In this study, Si porous pyramids nanostructures were synthesized by the metal-assisted chemical etching technique. Different KOH concentrations were used to develop high surface area Si porous pyramids for application as supercapacitor electrodes. Field-emission scanning electron microscope (FE-SEM) studies showed that 5% KOH solution will lead to high surface area Si pyramids with a specific capacitance of 90.3 F/cm². Silicon carbide (SiC) thin film was coated on Si pyramids (SiC@Si) using a facile sol–gel method followed by a carbothermal reduction process. Tetraethylorthosilicate and sugar were used as carbon sources. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and FE-SEM analysis were used to characterize the developed SiC@Si samples. The developed SiC@ Si electrode exhibited a high specific capacitance of 135.5 F/cm² at a scan rate of 10 mV/s (in 1 M NaOH electrolyte). The supercapacitor capability of this SiC@Si structure is significantly higher than classical materials. Because of its facile, controllable and efficient synthesis technique, this novel SiC@Si can be considered a very promising candidate for power sources applications.