Sorption of Aminonapht halene and Quinoline on Amorphous Silica

The adsorption of quinoline and aminonaphthalene was investigated from aqueous solution on amorphous silica SiO2. Amorphous SiO2 was not a strong adsorbent of these compounds and quinoline was adsorbed more strongly than aminonaphthalene. The adsorption of both compounds varied with pH. A maximum in adsorption occurred near their respective pKa\u27s. Temperature effects were significant, suggesting enthalpy contributions in the range of H bonding. Both compounds appeared to adsorb via identical mechanisms that included H bonding and ion exchange. The greater basicity of quinoline combined with (1) the enhanced electron-donating properties of the heteroatom N and (2) the delocalized Π-bonded ring system were proposed to account for its stronger adsorption. Aminonaphthalene showed greater exclusion from the internal region of porous SiO2, indicating that the compounds orient differently at the surface. The triple-layer adsorption model and three outer-sphere surface complexes were used to model the adsorption data. Good predictions of adsorption isotherms and the effects of ionic strength and electrolyte cation were obtained