Adsorption of di-2-pyridyl ketone salicyloylhydrazone on silica gel:: characteristics and isotherms

The adsorption of DPKSH onto silica gel was investigated, at 25 +/- 1degreesC and pH 1, 4.7 and 12. For the same DPKSH concentration interval, the minimum required time of contact for adsorption maximum at pH 4.7 was smaller than at pH 1 and the maximum amount of DPKSH adsorbed per gram of silica at pH 1 is smaller than at pH 4.7. At pH 12 the DPKSH adsorption onto silica gel was not significant. The adsorption data followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The maximum amount of solute adsorbed (m(ads)(max)) and the adsorption constant, K-L, were derived from Langmuir isotherm. The Freundlich constants 1/n and K-F related, respectively, to the energetic heterogeneity of adsorption sites and an empirical constant were evaluated. The mean sorption free energy (E) of DPKSH adsorption onto silica gel was calculated from D-R isotherm indicating a physical adsorption mode. Finally, conductimetric titrations showed the silica particle basicity and acidity as 0.002 and 0.3 mmol g(-1), respectively. (C) 2004 Elsevier B.V. All rights reserved.