ADSORPTION OF 1-ALKYL-4-METHYLPYRIDINIUM SALTS AT SOLID-LIQUID AND WATER-AIR INTERFACES

Determinations of the adsorption at both solid-liquid and water-air in terfaces of 1-alkyl-4-methylpyridinium salts have been performed. At t he water-air interface, measurements of the surface tension as a funct ion of the bulk concentration of 1-dodecyl-4-methylpyridinium chloride were performed. Mathematical treatment of the resulting isotherm allo wed the size of the adsorbed molecule and the CMC to be obtained. The solid adsorbent was a titanium dioxide sample prepared in the laborato ry. Adsorption isotherms of 1-dodecyl-4-methylpyridinium chloride and 1-butyl-4-methylpyridinium chloride were obtained at the same pH and i onic strength. For the shorter-chain surfactant, a second isotherm at a higher base electrolyte concentration was obtained. The experimental isotherms are discussed in the light of literature results and analyz ed on the basis of the Frumkin-Fowler-Guggenheim adsorption equation. X-ray photoelectron spectroscopic analyses were performed both on the bare adsorbent and in the presence of the adsorbates. The binding ener gy of the surfactant elements (both nitrogen and carbon) was observed to undergo significant modifications when the compound was in the adso rbed state. The features of the adsorption of the two organic ions are discussed in light of the different experimental results.