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

The adsorption of DPKSH onto silica gel was investigated, at 25±1 °C 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.