Adsorption Isotherm Models, Kinetics Study, and Thermodynamic Parameters of Ni(II) and Zn(II) Removal from Water Using the LbL Technique

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 8HQin"methanol > ethanol >1-propanol >1butanol > 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.