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The layer-by-layer technique (LbL) is an efficient and sustainable low-cost methodology for the removal of heavy metal ions from various matrixes. The present work is focused, for the first time, on the evaluation of the extraction processes of Ni­(II) and Zn­(II) by the LbL technique with respect to the studies of the solvent effect, reaction kinetics, adsorption isotherm models and thermodynamic parameters. The extraction of Ni­(II) and Zn­(II) was based on the design of multilayers of these metal complexes with 8-hydroxyquinoline (8HQ) due to the formation of Ni­(8HQ)2 and Zn­(8HQ)2 complexes, respectively. The efficient sorption of metal ions was found to follow the dissolution order of 8HQ in methanol > ethanol >1-propanol >1-butanol > acetonitrile. The surface adsorptive removal processes of Ni­(II) and Zn­(II) from aqueous solution were evaluated by four different kinetics models and were found to be better fit to the pseudo-second-order model with R 2 corresponding to 0.9891 and 0.9995, respectively. The intraparticle diffusion kinetics model was employed to confirm thin film production in the form of boundary layers to account for the removal processes of Ni­(II) and Zn­(II) from aqueous solution using the LbL technique as a diffusion-controlled process. The adsorption of Ni­(II) and Zn­(II) in the LbL technique was found to fit better with the Langmuir, Freundlich, and Temkin adsorption isotherm models. The thermodynamics parameters of Ni­(II) and Zn­(II) extraction from aqueous solutions confirmed the spontaneous and endothermic behavior of the adsorption process.

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A glass electrode-AgC1 cell, measured to kO.01 mV, has been used in evaluations of pK values at 25°C of four acids in the range pK 1-2.2. The practical work consisted of calibrating the cell with dilute HCl followed by additions of stock solutions containing the acid ligands. Three of the acids have been previously studied with Pt, H2-AgC1 cells so critical comparisons are possible.Attempts have been made to reduce the dependence of the pK values at zero ionic strength (when these are -c 2.5) upon the value of the ion-size parameter p used in the Debye-Huckel activity coefficient expression. The present calculations are based upon the use of a second parameter Q. Round values of this at different values of have been calculated from some HCI, salt data. A second but smaller feature which has been taken into account is the observations of Bates that standard electrode potentials (E") vary slightly with p if E" is derived by linear analysis. By using these two factors, (method C of table 3) the pK against p dependence is markedly diminished. Also, by using the p and Q parameters appropriate to HCl solutions, pK values close to the averages of those obtained by method C are obtained.For acids of pK values < 2.5, the values at zero ionic strength are markedly dependent upon the value assigned to p in eqn (2) when Q = 0. The dependence is much greater than is found with other methods such as conductivity 3* and the root

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The kinetics of aquation of bromopentaamine cobalt(III) complex have been investigated spectrophotometrically in aqueous-organic solvent media using acetonitrile, urea, and dimethyl sulfoxide as co-solvents at 45 ≤ T ( • C) ≤ 65. The logarithms of rate constant of the aquation reaction vary nonlinearly with the reciprocal of the dielectric constant for all cosolvent mixtures, indicating a specific solute-solvent interaction. Also, the rate constants are correlated with the total number of moles of water and the organic solvents. However, the solvent effects on the solvation components of the enthalpy of activation, H ‡ , and the entropy of activation, S ‡ , have been studied. Analysis of the solvent effect confirmed a common I d mechanism for the aquation of the cobalt(III) complex. C

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