Gehan M. Nabil

Improved removal and decolorization of C.I. anionic reactive yellow 145 A dye from water in a wide pH range via active carbon adsorbent-loaded- cationic surfactant

AbstractA fast and highly efficient method was developed for decolorization of C.I. anionic reactive yellow 145 A dye from wastewater under a wide pH range (1.0–13.0) using a loaded cationic surfactant on the surface of an active carbon adsorbent (HTAB-AC). The efficiency of dye removal by the proposed adsorbent was studied by the batch equilibrium technique under the influence of various controlling experimental factors such as adsorbent dosage, contact time, and initial dye concentration. The determined percentage removal values of reactive yellow 145 A dye by (HTAB-AC) adsorbent in the examined solutions were found 92.5–99.6, 90.7–98.1, and 88.5–96.9% for 120, 150, and 180 mg L−1 solutions, respectively. The equilibrium of removal (93.0–96.0%) was established at 20.0 min of shaking time. The effects of other system variables were evaluated and the adsorption behavior was investigated by the Langmuir and Freundlich models. Adsorption kinetic data were tested using pseudo-first-order, pseudo-second-order...

Micellar Effects on Alkaline Hydrolysis of 3,5-Dinitro-2-chloro Benzotriflouride and 2,4-Dinitrochloro Benzene in Aqueous-Acetonitrile Mixtures

Reaction rate for alkaline hydrolysis of the substrates 3,5-dinitro-2-chloro benzotriflouride (DNCBTF) (1) at 30°C and 2,4-dinitrochloro benzene (DNCB) (2) at 50°C separetely with NaOH as nucleophile is carried out spectrophotometrically in mixed aqueous-acetonitrile solvents. In each system, cationic surfactant as dodecyltrimethyl ammonium bromide (DoTAB), or anionic one as sodium dodecyle sulfate (SDS) is used in wide range of concentrations to study the effect of micelle on the reaction rate. The micellar effect is explained in term of modified pseudo phase ion exchange model. Pseudo first order rate constant, kobs is obtained for each of the nucleophile and for both substrates 1 and 2 at all range of XAN · kobs at given [OH−] and in presence of any substrate is found to increase with the increase of DoTAB,while decrease with the increase of SDS as micellar phases. Critical micelle concentrations (CMCs) in similar trend are observed to increase in DoTAB while decrease in SDS systems by increasing acetonitrile (AN) content. Micellar binding constant (KS) between any type of given substrate and the formed micelle, is found to decrease in presence of DoTAB and increase in SDS micellar phases by increasing AN content. Finally, the ratios between pseudo first order rate constants for hydrolysis in micellar phase kM to that in the bulk phase kw for DoTAB and SDS systems are found to be greater than and smaller than unity respectively at any given XAN where the data indicated for (1) is always higher than those for (2). The results concluded that micelle DoTAB is working as a catalyst for the reaction rate, while that for SDS is considered as an inhibitor.

Micellar Characters for Hydrolysis of Benzotrifluoride Derivative in Acetonitrile-Water Mixtures

The alkaline hydrolysis of 2-chloro-3,5-dinitrobenzotrifluoride (CDNBTF) as substrate in presence of the cationic surfactant dodecyl trimethylammonium bromide (DoTAB) above its critical micelle concentration (cmc) is studied spectrophtometrically at different acetonitrile (AN) -water mixtures and at different temperatures. Pseudo first order rate constant is found to increase by increasing the mole fraction of acetonitrile XAN in presence of the micelle indicated that micelle is catalyzed this reaction. The reaction is carried out in presence of adding NaBr, shown to decrease the rate of this reaction due to repelling the substrate from the micellar area causes salting out effect. Binding constant (KS) between micelle and the substrate at different XAN as well as solvatochromic properties of the given solutions are discussed. 1H NMR at only 50 and 80 AN-D2O v/v % are carried out to test the substrate orientation near micelles.

Hydrophobic effect for anionic dye - cationic surfactant interaction in aqueous and mixed solvent

Abstract The interaction between anionic dyes [Reactive Orange 122 (R.O 122), Reactive Blue 19 (R.B 19), Reactive Violet 5 (R.V 5) and Acid Green 20 (A.G 20)] with cationic surfactant cetyltrimethylammoniun bromide (CTAB) has been investigated by spectrophotometry and conductance technique. The used dyes are characterized by tautomeric behavior which affects the mechanism of the interaction. Various parameters such as dye structure, surfactant composition, solvent composition, temperature and pH of the medium were studied. The spectral data were applied for calculating the binding constant between dye and surfactant (Kb), fraction of micellization (ƒmic), and standard free energy change of binding (ΔG°b) in 0,10,20 and 30 v/v % acetonitile (AN). Conductance technique was constructed to estimate the ion pairing constant (Ka) at different temperatures and v/v % AN. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) for ion pair formation were evaluated. The role of hydrophobic and electrostatic effect on dye-surfactant interaction was discussed. Graphical Abstract The interaction between anionic dyes [Reactive Orange 122 (R.O 122), Reactive Blue 19 (R.B 19), Reactive Violet 5 (R.V 5) and Acid Green 20 (A.G 20)] with cationic surfactant cetyltrimethylammoniun bromide (CTAB) has been investigated by spectrophotometry and conductance technique. Visible spectra(a) and specific conductance (b) of R.O122-CTAB system in 10% v AN at 25 °C (dye concentration 1x10−4 mol L−1) CMC of R.O122/CTAB =1.2x10−4molL−1.Key words: dye structure, solvent composition, spectral character, hydrophobic effect, conductance.

Kinetics of the Micellar Effects on the Alkaline Hydrolysis of 2-Chloro-quinoxaline in Acetonitrile-Water Mixtures at 35°C

Pseudo-first-order reaction rate for alkaline hydrolysis of 2-chloroquinoxaline (2-CQX) is carried out in acetonitrile (AN)-water (H2O) mixtures at 35°C. Cationic surfactants as dodecyltrimethylammonium bromide (DOTAB) and an anionic surfactant as sodium dodecylsulphate (SDS) are used above their critical micelle concentration (cmc) to study the effect of micelles on reaction rate. When increasing the percentage of volume of AN, the rate profiles with DOTAB are shown to slightly increase with increasing surfactant concentration, while that with SDS are found to smoothly decrease. The micellar effect is explained in terms of a modified pseudo-phase ion exchange model. The binding constant (KS) between 2-CQX and DOTAB as micelle showed a decrease by increasing percentage of volume of AN, while that with SDS increased. The counterion micellar coverage degrees (β) are found to be 0.55 and 0.85 with DOTAB and SDS systems, respectively, at all range of volume percentage of AN. Finally, the calculated ratio between rate constants in water to that in the micelle region kw/kM at different volume percentage of AN indicated that DOTAB enhances the reaction rate while SDS inhibits it.