Shehata M. Zourab

Nanostructured copper oxide-cotton fibers: synthesis, characterization, and applications

Copper oxide nanoparticles were prepared and subsequently deposited onto surface of the cotton fibers by ultrasonic irradiation. The structure and morphology of the coated and un-coated cottons were examined by X-ray diffraction and scanning electron microscopy/energy dispersive X-ray analysis. These methods revealed that of CuO nanoparticles are crystalline and corresponds to monoclinic phase, and that these nanoparticles are physically adsorbed onto the cotton fiber surface. They have an average crystallite size of 10 nm; the physical and chemical properties of the treated cotton fibers are markedly different from those of the untreated cotton fibers. The CuO-cotton fiber nanocomposites were tested against Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive) cultures and showed a significant antimicrobial activity; whereas its analogous CuS-coated cotton material formed by the reaction CuO-coated cotton fibers with H2S showed no activity.

Encapsulation of Phenolphthalein pH-Indicator into a Sol-Gel Matrix

Transparent monolithic silica doping with phenolphthalein has been prepared via the acid-catalyzed sol-gel reactions of tetraethylorthosilicate in the presence of phenolphthalein. The immobilized phenolphthalein pH-indicator shows similar behavior as its solution counterpart. The UV/Vis spectra indicate that the phenolphthalein retains its structure during the sol-gel reactions in terms of response to pH. The phenolphthalein can be regarded as uniformly distributed in the silica matrix. This observation has been confirmed using polarized microscopy.

Encapsulation of Methyl Red pH‐Indicator into a Sol‐Gel Matrix

Encapsulation of methyl red pH indicator into transparent monolithic silica matrices was made via the acid‐catalyzed sol‐gel reaction of tetraethylorthosilicate and methyl red indicator. The immobilized methyl red shows behavior similar to its solution counterpart. It retains its structure during the sol‐gel reactions in terms of response to pH. Polarized light microscopy and the surface morphology indicated that methyl red molecules are strongly interacted within the host silica network.

Behaviour of phenol red pH-sensors in the presence of different surfactants using the sol-gel process

Phenol red was immobilised into a polysiloxane matrix using a sol-gel process to form pH optical sensors. The sol-gel was obtained by hydrolysis of tetraethoxysilane (TEOS) in the presence of phenol red (PR) and the appropriate surfactant. Different surfactants, namely cetyltrimethylammonium bromide (CTAB), dodecyldimetyl amino-oxide (GLA) and Triton X-100 (TX-100), were employed. Interestingly, the use of surfactants significantly improved the mesostructure of the silica and increased the porosity of the system. The two response pH ranges were shifted to pH 0.0–3.0 and pH 10.5–1.5M [OH−] compared with those of the free PR (pH 0.0–3.0 and pH 6.5–9.5). It is found that the pH response and the pKa shift of the phenol red were dependent, not only on the silica matrix but also on the ionic properties of surfactants. In the case of ionic surfactants such as CTAB or GLA, there was further shift to more acidic and more basic pH, whereas in the case of non-ionic surfactants such as TX-100 no significant change of the pH curve was observed.

Oxidation of Amines by Potassium Ferricyanide in AOT Surfactant Systems

Abstract The kinetic and catalytic oxidation of dibutylamine(DBA), diethyl‐amine(DEA), dipropylamine(DPA), ethylamine(EA), ethylmethylamine(EMA), propylamine (PA), triethylamine(TEA), and trimethylamine(TMA) by 0.001 M potassium ferricyanide in the presence of 0.03 M NaOH at 25°C in aqueous and/or in and 0.003 M sodium dioctylsulfosuccinate (AOT) have been studied using visible spectrophotometry at 420 nm. The present data show that the reaction is first‐order with respect to [amine]T and [Fe(CN)6]3−. Also, the k obs have constant values over 0.015–0.05 M NaOH and decrease below the CMC (of AOT) and increase above the CMC. The characteristics of reaction have been studied in the presence of different salts with common cation or anion. It was observed that in aqueous solution, the k obs values increase with increasing salt concentration for both (0.005–0.06 M) common cation and (0.1–0.6 M) for common anion. But in the presence of AOT, values of k obs initially decrease up to 0.015 M for both types of salts, and then increase above 0.015 M salt. The thermodynamic parameters ΔG*, ΔH*, and ΔS* have been calculated. The pseudophase model has been applied to the system and binding constants of amine to AOT micelles have been calculated. These values correlate with the respective reactivities in aqueous AOT.

Thin film optical BTB pH sensors using sol–gel method in presence of surfactants

Bromothymol blue (BTB) thin films were prepared by depositing a thin layer of a solution containing tetraorthosilicate and BTB pH indicator in the presence of surfactants, namely cetyltrimethylammonium bromide (C19H42BrN, CTAB) or dodecyldimethylamine oxide (C14H31NO, 69%), C16H35NO (11%), Genaminox LA onto a glass slide substrate. CTAB or GLA surfactants were used to improve the mesostructure of the host material and to increase its porosity. Optical BTB thin films were found to be sensitive against pH and behave as free BTB. This provides evidence for weak interactions between the BTB molecules and the host silica matrix. The effects of the sol mixture on the stability and reproducibility and the colorimetric response to solutions of different pH were examined and pKa values were determined. The BTB thin film sensors showed an advantage over the encapsulated monolithic sensors in which the thin film sensors exhibit a faster response time than the monolithic disks. These pH sensors showed reproducibility and high stability behavior.

Spectrophotometric Studies of Entrapped Thymol Phtalein pH Indicator into Sol‐Gel Matrix

This research involves the behavior of thymol phtalein pH indicator entrapped into the sol‐gel derived inorganic matrix. The method is based on the physical entrapment of the reagent molecules in the sol‐gel matrix. The immobilized thymol phthalein pH indicator shows behavior similar to its solution counterpart. The UV/vis spectra indicate that the thymol phthalein retains its structure during the sol‐gel reactions in terms of response to pH. Thymol phthalein can be regarded as uniformly distributed in the sol‐gel matrix. This observation has been confirmed using polarized microscopy. This research shows that thymol phtalein can be immobilized in sol‐gel glasses and used as a solid pH sensor.

Phase Behavior of Dodecyl Dimethyl Amino Oxide/Sodium Dodecyl Sulfate in the Presence of Perfluorooctanol

The ternary phase diagram of dodecyl dimethyl amino oxide (C12DMAO) perfluorooctanol (C7F15CH2OH) – H2O, sodium dodecyl sulfate (SDS) – (C7F15CH2OH) – H20, C12DMAO/SDS (66/33, w/w) – (C7F15CH2OH) – H20, and C12DMAO/SDS (33/66, w/w) – (C7F15CH2OH) – H20 systems have been studied. The identification of the phases was done by macroscopic observation of the sample either by naked eye or through crossed polarizers. For further characterization of the phases, different techniques were used such as electrical conductivity, polarization microscopy, 2H-NMR, and small angle X-ray scattering. The microstructure resulting from the self assembly of the surfactant can vary from normal micelle (L1), lamlar liquid crystal (Lα), to reverse micelles (L2), as relative volume fraction of apolar component increases over that of polar component.

Electrochemical Degradation of Herbicidal and Pure 2,4-Dichlorophenoxy Acetic Acid on Pb/PbO2 Modified Electrodes

Lead/lead oxide Pb/PbO2 modified electrodes was prepared for electrocatalytic oxidation of agrochemicals including herbicidal 2,4-D (albar super) and pure 2,4-dichlorophenoxy acetic acid. The results of electrocatalytic oxidation process of the agrochemical solutions were expressed in terms of the remaining concentration and COD removal. The different operating conditions of treatment process were investigated including current density, pH, temperature, time of electrolysis, type of conductive electrolyte, and its specific conductance. This electrode gives good results for the removal of agrochemicals and COD. Also, the results showed the best conductive electrolytes is NaCl. This observation was attributed to the small size of Na+ and contribution of Cl− ion in formation of OCl−.

Phase Diagram and Effect of Additives on the Behavior of Alkyldimethyl Amine Oxide Mixture

Abstract The phase diagram for the Genaminox 1216 (a zwitterionic surfactant), pentanol‐water system has been constructed at 25°C. The sequence of the phases varies from L1, L1*/Lα, Lα, two phases and L2 as the system was made more lipophilic. Identification of the phases was done by means of crossed polarizer, electrical conductivity and optical polarizing microscopy techniques. Through surface tension measurements, a critical micelle concentration (CMC) of 9 × 10−4 M for the surfactant in aqueous solution was determined. Aromatic salts (such as sodium salicylate and sodium benzoate) reduce the value of this CMC more than aliphatic salts (a sodium citrate and sodium oxalate).This behavior indicates that aromatic salts promote the surfactant assembly more than aliphatic salts. Methyl orange (MO) was used as a solvatochromic reporter to study the nature of interaction of additives with the surfactant by using a UV‐vis technique. The λmax absorption band for aqueous MO has a peak at 463 nm. A blue shift in λmax was observed either in the presence of surfactant (above the CMC) or in surfactant‐salt solution.