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Sorption of Metal Ions at the Oxide/Liquid Interface

Parveen, Shahida (2002) Sorption of Metal Ions at the Oxide/Liquid Interface. PhD thesis, University of Peshawar, Peshawar .

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Abstract

A detailed study of the surface and adsorption properties of zinc oxide was undertaken. The compound (ZnO) was first identified and characterized by X-ray diffractometry, FTIR analysis, surface area and electron probe microanalysis. Point of zero charge and surface acidity constants were determined in the temperature range 293-323K, using a fast titration technique. Point of zero charge (PZC) and the surface acidity constants (pKa1 and pKa2) were found to decrease with increasing temperature. The values of the dissociation constants (pKa1 and pKa2) determined from the Henderson - Hasselbach equation agreed very well with those determined using the Gaines- Thomas equation. The thermodynamic parameters ⌂Ho and ⌂So for the processes were also evaluated. A comprehensive study of the potentiometric titration's of zinc oxide in the presence of Zn(II), Ni(II), Co(II), Ba(II). Ca(II), and Mg(ll) was undertaken under different experimental conditions of temperature, concentration and pH. Stability constants of the metal surface complex species. resulted front the adsorption reaction, were evaluated by a simplified Gains-Thomas equation. The pK values obtained were in the order Zn(II) > Ni(II) > Co(II) > Ba(ll) > Ca(I I) > Mg(ll). Thermodynamic parameters AGO, AH° and AS° were also investigated. The adsorption isotherms of Zn(II), Ni(II), Co(II), Mg(II) and Ca(ll) on zinc oxide from aqueous electrolyte solution have been investigated as a function of solution concentration, pH and temperature. The adsorption behaviour in each case was of the Langmuir type. Thermodynamic parameters such as ⌂Go, ⌂Ho and ⌂So of adsorption were computed and interpreted. The extent of adsorption was found to increases with the increase of pH and concentration and decrease of temperature. The affinity of the metal ions towards the oxide surface was found to be in the order Zn(II) > Ni(II) > Co(ll)> Ca(II) and > Mg(ll). The isosteric heat (AH) of Ni(II) adsorption was computed between 303K and 323K. All' was found to increase with the increase in the extent of adsorption indicating a decrease in the extent of the heat evolved in the process. FTIR spectra of ZnO before and after sorption of metal ions as a function of pH and solubility product calculations showed the formation of a double hydroxide, on the surface which resulted in the reduction of the dissolution of the zinc oxide. The kinetics of both metal cations sorption on ZnO and the surface dissolution were studied at different temperatures (303K - 323K). The decrease in the extent of adsorption of the metal cations with temperature was due to the distraction of the surface on account of the dissolution of the ZnO. The value of energy of activation determined from an empirical relationship was found to be 68.10 kj/mol, which is almost equal to the combined value of 66.27 kj/mol for the adsorption of metal ions and dissolution of ZnO.

Item Type:Thesis (PhD)
Uncontrolled Keywords:Sorption, Metal, Ions, potentiometric titration's, zinc, Oxide/Liquid, Interface
Subjects:Physical Sciences (f) > Chemistry(f2)
ID Code:6813
Deposited By:Mr. Javed Memon
Deposited On:28 Jul 2011 09:57
Last Modified:28 Jul 2011 09:57

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