A new renewal approximation for certain autocorrelated processes

We propose a new renewal approximation for autocorrelated streams with limiting index of dispersion less than unity. The superposition of independent processes and the splitting of an autocorrelated process are studied. The proposed approximation performs well on predicting the mean delay in a single server queueing system receiving autocorrelated processes.     

Graphene oxides/multi-walled carbon nanotubes hybrid-modified carbon electrodes for fast and sensitive voltammetric determination of the anticancer drug 5-fluorouracil in spiked human plasma samples

The electrochemical oxidation of anticancer drug 5-fluorouracil (5-FU) at graphene oxides (GOs)/carbon nanotubes (CNTs) nanohybrid-modified screen-printed carbon and glassy carbon electrodes was studied by voltammetric techniques. The modified electrodes showed better performance toward the electro-oxidation and determination of 5-FU compared to CNTs-modified or GOs-modified electrodes. The oxidation peak current obtained at about + 1.156 V (vs. Ag/AgCl) from square wave voltammetry was linearly dependent on the 5-FU concentration in the ranges of 0.05–5 and 5–1200 µM in phosphate buffer solution of pH 7.0. The developed method was applied successfully to the electrochemical sensing of 5-FU in human plasma samples at micro-molar concentration levels with satisfactory results. It is hopeful that the developed method in the future can be used for the simple and fast determination of 5-FU in clinical test and pharmacokinetics.     

Selective separation of yttrium(III) through a liquid membrane system using 2-thenoyltrifluoroacetone as an extractant carrier

2-Thenoyltrifluoroacetone has been offered as a mobile carrier in organic phase for the transport and selective separation of yttrium from aqueous media using a liquid membrane system. Perceivably, the use of n-propylamine (PA) in the source phase enhances the transport of yttrium ions. The extraction and stripping conditions have entirely been evaluated and explained. The suggested method has been utilized for the separation of yttrium(III) from its binary mixtures with strontium(II) and some other cations such as Ni²⁺, Co²⁺, Ag⁺, Fe²⁺, Al³⁺, Cu²⁺, Hg²⁺and Cs⁺ in aqueous solutions of pH 5.4 in the presence of PA, while 1 M nitric acid was acting as a stripping agent in the receiving division. Cyanide ion and 5-sulfosalicylic acid have been used as masking agents to minimize the interferences from different transition metal ions and Al³⁺ in the source phase, respectively. ⁹⁰Y in secular equilibrium with ⁹⁰Sr in the source phase, was transferred to receiving phase and separated completely from its long-lived parent isotope. The activity of the transported ⁹⁰Y was found to decay with a half-life 64.17 ± 0.05 h. The purity of yttrium-90 was comparable or better than the other applied liquid membrane systems for purification of yttrium-90.     

Preparation and characterization of a new CdS–NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/reduced graphene oxide photocatalyst and its use for degradation of methylene blue under visible light irradiation

In this paper, CdS nanoparticles as a visible light active photocatalyst were coupled by NiFe₂O₄ and reduced graphene oxide (rGO) to form CdS–NiFe₂O₄/rGO nanocomposite by facile hydrothermal methods. The CdS–NiFe₂O₄/rGO nanocomposite shows enhanced photocatalytic activity for the degradation of methylene blue (MB) under visible light illumination. In addition to improved photocatalytic performance, this prepared nanocomposite shows increased photostability and is magnetically separable from the aqueous media. The degradation rate constant (k_app) of the optimized photocatalyst, i.e. CdS–NiFe₂O₄ (0.05)/rGO 25 wt% nanocomposite, was higher than the corresponding CdS and NiFe₂O₄ nanoparticles by factors of 11.1 and 8.9, respectively. The synergistic interactions between CdS, NiFe₂O₄ and rGO lead to enhanced surface area, reduced aggregation of the nanoparticles, decreased the recombination of photogenerated electron–hole pairs, and increased the charge separation efficiency and effective electron–hole generation transfer. According to the obtained results, a proposed mechanism of the photodegradation of MB under visible light irradiation is finally mentioned.     

Synthesis of 3-aminoisoxazolmethylnaphthols via one-pot three-component reaction under solvent-free conditions

A one-pot three-component condensation reaction of 3-amino-5-methylisoxazole, aryl aldehyde and 2-naphthol to afford the corresponding 3-amino isoxazolmethylnaphthols in good to excellent yields. The remarkable features of this new procedure are high conversions, clean reaction condition, short reaction time, nonhazardous and environmentally friendly reaction condition, inexpensive and easily commercially availability of the catalyst and simple work-up procedures.     

Synthesis of nanostructured titania/zirconia membrane and investigation of its physical separation and photocatalytic properties in treatment of textile industries wastewater

Nanostructured TiO₂/ZrO₂ composite membranes with varying compositions were obtained by sol–gel technique. The influence of 0–30 mol% zirconia doping on microstructure, water permeability, photocatalytic and physical separation properties, removal of methyl violet of textile industries wastewater and thermal and mechanical stability of titania/zirconia composite membranes was described. Firstly, alumina supports were coated with TiO₂ intermediate layers using the colloidal sol–gel route. The TiO₂/ZrO₂ composite sols were prepared via a polymeric sol–gel method and dip-coated on TiO₂ intermediate layer. The samples were characterized by DLS, TG-DTA, XRD, FTIR, BET-BJH, UV–visible, SEM, TEM and AFM. It was shown that zirconia retards the phase transformation of anatase to rutile until at least 700 °C. The minimum pore size and maximum surface area obtained were 1.2 nm and 153 m²/g, respectively, attributed to the sample with 20 mol% zirconia. The mechanical strength of titania membranes was significantly improved by addition of zirconia. The most methyl violet removal efficiency obtained, with and without UV-irradiation, is 80.8 and 72.6%, respectively, attributed to the sample with 20 mol% zirconia.     

Complex formation of hydronium ion with several crown ethers in 1,2-dichloroethane,acetonitrile, and nitrobenzene solutions

A conductance study concerning the interaction between hydronium ion and several crown ethers in acetonitrile, nitrobenzene and 1,2-dichloroethane solutions has been carried out at 25°C. The stability constants of the resulting 1:1 complexes in acetonitrile and nitrobenzene solutions were determined from the molar conductance-mole ratio data and found to vary in the order 18C6>DB30C10>DC18C6>DB18C6>DB21C7>DB24C8>B15C5. In 1,2-dichloroethane solution, the complexation process results in the dissociation of ion pairs. There is an inverse relationship between the stabilities of the complexes and the Gutmann donicity of the solvents. In nitrobenzene solution, some evidence for the formation of a 2:1 sandwich adduct between the smaller crowns (i.e., B15C5 and 18-crowns) are observed from the molar conductance-mole ratio data which is supported by the¹H NMR data.     

Synthesis of 4′-Carboxy-benzo-30-crown-10 and a Thermodynamic Study of Its Complexes with Thallium and Alkali Cations in Acetonitrile Solution

A synthetic procedure has been developed for the preparation of 4-carboxy-benzo-30-crown-10. The formation of Na+, K+, Rb+, Cs+ and Tl+ complexes with the large crown ether was investigated conductometrically in acetonitrile solution at various temperatures. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data. It was found that the stability of the complexes vary in the order Tl+ > K+ > Rb+ > Cs+ > Na+. The data obtained in this study support the existence of a wrap around structure for the above complexes in solution. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. In all cases, the complexes were enthalpy stabilized but entropy destabilized. The resulting TS° vs. H°plot showed a fairly good linear correlation, indicating the existence of an entropy-enthalpy compensation in the large crown complexation reactions.     

Simultaneous determination of phenol and mononitrophenol isomers using PLS regression and conventional and derivative spectrophotometry

The partial least squares regression method (PLS) was tested as a calibration procedure for the simultaneous determination of phenol, o-nitrophenol, m-nitrophenol and p-nitrophenol by both conventional and first derivative UV/Vis spectrophotometry. The experiments were conducted in the acidic, neutral and basic media. The results obtained by the application of the PLS procedure on the conventional and first derivative spectra in two solvent media were compared. It was found that the results obtained in the basic medium have better performance characteristics than those obtained in the acidic or neutral media. Comparable results were obtained in the case of both conventional and first derivative absorbance data. The proposed method was applied to the determination of the four phenol derivatives in natural spiked water samples at concentration levels between 1.0 and 10.0 microg ml(-1) with average recoveries in the range 96% - 99%.