A potentiometric rhodamine-B based membrane sensor for the selective determination of chromium ions in wastewater.

The construction and performance characteristics of a novel chromate ion-selective membrane sensor are described and used for determining chromium(III) and chromium(VI) ions. The sensor is based on the use of a rhodamine-B chromate ion-associate complex as an electroactive material in a poly(vinyl chloride) membrane plasticized with o-nitrophenyloctyl ether as a solvent mediator. In a phosphate buffer solution of pH 6 - 7, the sensor displays a stable, reproducible and linear potential response over the concentration range of 1 x 10(-1) - 5 x 10(-6) mol l(-1) with an anionic Nernstian slope of 30.8 +/- 0.5 mV decade(-1) and a detection limit of 1 x 10(-6) mol l(-1) Cr(VI). High selectivity for Cr(VI) is offered over many common anions (e.g., I-, Br-, Cl-, IO4-, CN-, acetate, oxalate, citrate, sulfate, phosphate, thiosulfate, selenite, nitrate) and cations (e.g., Ag+, Ca2+, Sr2+, Co2+, Ni2+, Cu2+, Mn2+, Fe2+, Zn2+, Cd2+, Al3+, Cr3+). The sensor is used for determining Cr(VI) and/or Cr(III) ions in separate or mixed solutions after the oxidation of Cr(III) into Cr(VI) with H2O2. As low as 0.2 microg ml(-1) of chromium is determined with a precision of +/-1.2%. The chromium contents of some wastewater samples were accurately assessed, and the results agreed fairly well with data obtained by atomic absorption spectrometry.     

Structural characterization,thermal, DFT,cytotoxicity, and antimetastatic properties of cocaine complexes with La(III), Er(III), and Yb(III)

Research on Chemical Intermediates - Reaction of cocaine (Cn) with Ln(III) chloride salts [where Ln?=?La(III), Er(III), and Yb(III)] afforded complexes of the [Ln(Cn)Cl(OH2)3].2Cl type...     

Natural convection in a porous medium coupled across an impermeable vertical wall with film condensation

This paper presents a theoretical study of thermofluid interaction between natural convection in fluid-saturated porous medium and film condensation, coupled through an impermeable vertical wall. The two heat transfer modes are analyzed separately. The solutions are matched on the wall. The complexion of this two-fluid problem is governed by a dimensionless interaction parameter which relates the heat transfer effectiveness of the two heat transfer mechanisms. The effect of this parameter on the flow and heat transfer is documented. Results regarding the overall heat transfer coefficient are obtained for a wide range of the independent parameters. Received on 19 January 1998     

Laminar forced convection conjugate heat transfer over a flat plate

Coupled heat transfer between laminar forced convection along and conduction inside a flat plate wall is theoretically studied. The laminar convective boundary layer is analyzed by employing the integral technique. The energy equations for the fluid and the plate wall are combined under the condition of the continuity in the temperature and heat flux at the fluid-solid interface. The analysis results in a simple formal solution. Expressions have been obtained for calculating local Nusselt number, wall heat flux and temperature along the plate, all are functions of the local Brun number, Br _x , which is a measure of the ratio of the thermal resistance of the plate to that of the convective boundary layer. The results indicate that for Br _x ≥0.15, neglecting the plate resistance will results in an error of more than 5% in Nusselt number. Comparison of the present solution with other previous studies has been made. The solution may be of a considerable theoretical and practical interest. Received on 19 August 1998     

Effect of KOH molarity and annealing temperature on ZnO nanostructure properties

In this work, ZnO nanorods (NRs) were fabricated using a low cost chemical bath deposition (CBD) method. The effect of the potassium hydroxide concentration on the fabricated ZnO nanostructures was studied in depth. The optical, structure, and surface morphology properties of the fabricated ZnO nanostructures were investigated using Uv-vis spectroscopy, XRD, and SEM. The results indicate that the formation of hexagonally structured ZnO nanorods with different lengths and diameters was dependent on the KOH concentration. The sample prepared with 2 M of KOH was the best one for optoelectronic applications, since it has the smallest diameters. This sample was annealed at different temperatures (473 K–1073 K). Positron Annihilation Lifetime Spectroscopy was used to determine the defects in the ZnO nanorods. The results show that the positron mean lifetime (τ_m) decreased as the annealing temperature increased, which means that the overall defects in the ZnO nanorods decreased with increasing temperature. Consequently, higher performance semiconductor devices based on ZnO nanorods could be fabricated after high annealing of the ZnO nanorods.     

Forced convection film condensation of flowing vapour on an inclined circular tube

In this work, an analytical study is made on the process of forced-convection-dominated laminar-film condensation on an inclined circular tube for a pure saturated vapour with vertical downflow. The resultant partial differential equation for the local film thickness has been solved analytically by applying the method of characteristics. Thus, an explicit analytical solution; in closed-form, has been obtained for calculating the local and average Nusselt numbers. The general solution yields, in special cases, the known analytical solutions of vertical and horizontal tubes. The results show that an optimum inclination of the tube, at which the rate of condensation on the whole surface is maximum, is a function of the ratio L/D. Received on 14 April 1999     

Thermal properties of pure and doped (polyvinyl-alcohol) PVA

Films ≈350 μm of poly(vinyl-alcohol) composites, containing copper (Cu), aluminium (Al) and iron (Fe), metallic powder very fine, were prepared by a casting method. Thermal conductivity, phonon velocity, mean free path and specific heat were studied. The pure sample of PVA has a lower values of thermal conductivity than that which are doped with metals. For all samples the thermal conductivityK increases up to a certain temperatureT _gg (120–160°C) and then decreases with temperature. The specific heat increase with temperature up to ≈120°C and above 120°C is nearly independent on temperature. The pure sample of PVA has small values of mean free path (L)≈0.2 Å at room temperature, but for PVA⁺ metalsL≈2.0 Å. The phonon velocity of pure PVA is larger than that of PVA containing metals.     

Dual Spinneret Electrospun Polyurethane/PVA-Gelatin Nanofibrous Scaffolds Containing Cinnamon Essential Oil and Nanoceria for Chronic Diabetic Wound Healing: Preparation,Physicochemical Characterization and In-Vitro Evaluation

In this study, a dual spinneret electrospinning technique was applied to fabricate a series of polyurethane (PU) and polyvinyl alcohol–gelatin (PVA/Gel) nanofibrous scaffolds. The study aims to enhance the properties of PU/PVA-Gel NFs loaded with a low dose of nanoceria through the incorporation of cinnamon essential oil (CEO). The as-prepared nCeO₂ were embedded into the PVA/Gel nanofibrous layer, where the cinnamon essential oil (CEO) was incorporated into the PU nanofibrous layer. The morphology, thermal stability, mechanical properties, and chemical composition of the produced NF mats were investigated by STEM, DSC, and FTIR. The obtained results showed improvement in the mechanical, and thermal stability of the dual-fiber scaffolds by adding CEO along with nanoceria. The cytotoxicity evaluation revealed that the incorporation of CEO to PU/PVA-Gel loaded with a low dose of nanoceria could enhance the cell population compared to using pure PU/PVA-Gel NFs. Moreover, the presence of CEO could inhibit the growth rate of S. aureus more than E. coli. To our knowledge, this is the first time such nanofibrous membranes composed of PU and PVA-Gel have been produced. The first time was to load the nanofibrous membranes with both CEO and nCeO₂. The obtained results indicate that the proposed PU/PVA-Gel NFs represent promising platforms with CEO and nCeO₂ for effectively managing diabetic wounds.     

Electrical conduction in copper-poly(vinyl-alcohol) composites

The temperature dependence of d.c. conductivity was investigated in composites of copper (Cu) and poly(vinyl-alcohol) (PVA) prepared by compression of a mixture. A minimum appeared in the conductivity vs reciprocal temperature curves, which is discussed as a result of the competition between hopping and thermally activated modes of conduction. It was also found that the conduction of Cu-PVA composites obeys a percolation model. Dependences of reverse current vs voltage were investigated and discussed in terms of a clean-up effect of charge carriers. Quantitative analysis was carried out to determine the activation energy, drift mobility and carrier concentration.