Ayman A. Issa

A simple and accurate analytical method for determination of three commercial dyes in different water systems using partial least squares regression

A simple analytical procedure is proposed for simultaneous determination of three common dyes (Basic Blue 9, Brilliant Blue E-4BA, and Reactive Blue 2) in natural waters without prior separation of the solutes. A popular chemometric method, partial least squares regression PLS-1, was effectively applied for spectral resolution of a highly overlapping system. At the best modeling conditions, mean recoveries and relative standard deviations (RSD) for dyes quantification by PLS-1 were found to be 102.1 (4.4), 95.7 (8.4), and 98.9 (6.2) for Basic Blue, Brilliant Blue, and Reactive Blue, respectively. The estimated limits of detection (LOD) were estimated using net-analyte signal concept and were 0.11, 0.52, 0.49 mg L(-1) for Basic Blue, Brilliant Blue, and Reactive Blue, respectively. The quantitative determination of dyes spiked in real water samples was carried out successfully by PLS-1 with satisfactory recoveries for dyes (90-106%).

Activation of kaolin with minimum solvent consumption by microwave heating

Abstract A kaolin clay was activated with 1.0 ᴍ H2SO4 solution at minimum liquid to solid ratio (L/S) using microwave heating. The optimum experimental conditions for activation were L/S ratio 3.0 mL 1 ᴍ H2SO4 per gram kaolin, microwave input power 500-600 W, and heating time 5-10 min. Activation at L/S < 3.0 mL/g using 1.0 ᴍ H2SO4 was not efficient, indicating the influence of solvent for absorbing microwaves more intensively and thus improving activation. Significant physicochemical changes were observed by the proposed procedure with smaller volumes of activator compared to the conventional heating method. Microwave input power and heating time have a strong influence on the quality of the final material; activation at high input power (>700 W) and longer heating times (>10 min.) are not recommended since they cause dissolution of kaolinite structure. Microwave-heated kaolin manifested better adsorption for tartrazine dye due to improvements in textural and chemical properties of kaolinite. Moreover, irradiation of used kaolinite has significantly improved dye desorption, increasing the importance of microwaves in regeneration/recycling studies. Detailed dielectric measurements of kaolin-acid mixtures recorded at frequencies much lower than 2.45 GHz revealed that absorption of radiation is highly dependent on the activator solution in the mixture. For 3.0 mL/g mixtures, high dielectric constant Ɛ’ 5223, dielectric loss factor Ɛ’’ 5083, tangent loss tan δ 1.30, penetration depth dp 0.57 cm at (103 Hz), and AC-conductivity σ 0.032 Ωm-1 were determined at 105 Hz. Filling the pores of kaolin by acid solution increased the microwave absorption and hence de-alumination of kaolinite.

Free energy perturbation and MM/PBSA studies on inclusion complexes of some structurally related compounds with β-cyclodextrin

Molecular dynamics (MD) simulations have been conducted to explore time-resolved guest–host interactions involving inclusion complex formation between β-cyclodextrin and organic molecules bearing two peripheral benzene rings in aqueous solution. Moreover, free energy perturbation (FEP) and thermodynamic integration (TI) methods at different simulation times have been employed to estimate the relative free energy of complexation. Also, the less computer-time demanding molecular mechanics/Poisson–Boltzmann surface area (MM/PBSA) method was used to estimate the free energy of complexation based on only 1-ns MD simulation. Results showed that both FEP and TI methods were able to reasonably reproduce the experimental thermodynamic quantities. However, long simulation times (e.g. 15 ns) were needed for benzoin mutating to benzanilide (BAN), while moderately shorter times were sufficient for BAN mutating to phenyl benzoate and for benzilic acid mutating to diphenylacetic acid. The results have been discussed in the light of the differences in the chemical structural and conformational features of the guest molecules. In general, it was apparent that the TI method requires less time for convergence of results than the FEP method. However, the less expensive MM/PBSA method proved capable of producing results that are in agreement with those of the more expensive TI and FEP methods.

Deposition of two natural clays on a Pt surface using potentiostatic and spin-coating techniques: a comparative study

Abstract Two natural clays (kaolinite and montmorillonite) were deposited onto a platinum electrode surface using two deposition techniques and under different experimental variables. For both clays, the percentages of surface coverage (%y) were optimized in the 75-96% range. A greater surface coverage was observed at higher temperatures for both clays, which confirms the endothermic nature of the deposition process. The maximum surface coverage (96%) was achieved for kaolinite. The surface coverage of kaolinite on a platinum electrode was constant for deposition times between 6 and 20 h. A surface coverage of 91% with montmorillonite particles was achieved. There was a very small increase in surface coverage by increasing the concentration of clay in the modified solution. The maximum surface coverage was observed under acidic conditions and smaller coverage values were reported for neutral and basic solutions. For both clays, a complete surface coverage for the electrode surface was achieved using the spin-coating technique. The experimental variables that affect the deposition of the clay, such as the stoichiometric ratio of clay/PVC and centrifugation speed and time, were studied and optimized to obtain full surface coverage. The spincoating method achieved the required durability and stability for the modified-electrode. The characterization showed that the metallic surface chemistry of the platinum electrode was totally suppressed. Both modified electrodes were found to be useful for determination of Ag(I) ion with a detection limit as small as 1.00×10-10 м. The analytical precision was also satisfactory (RSD <5.0%).