Adsorption of Surfactants on Activated Carbon in the Presence of Metallic Ions: Determination of the Adsorption Energy Parameters

The adsorption characteristics of various surfactants in the micromolar concentration range were determined in batch reactors using powdered activated carbon. The anionic sodium dodecylsulphate, the cationic hexadecyltrimethylammonium bromide and benzyldimethyldodecylammonium bromide, and the non-ionic nonylphenoxyheptaethoxyethanol were used as model molecules. The influence of sodium and calcium ion concentrations on the adsorption equilibrium parameters and on the energy of adsorption for surfactants was investigated using the Langmuir and the Deiylo-Jaroniec equations. Results showed that inorganic cations enhance adsorption of all surfactants, primarily by the diminution of repulsives interactions between the negative functional groups of the carbon surface and the ionized or polar groups of the surfactants. Results for energy of adsorption indicate that hydrophobic interactions, rather than ionic interactions, are mainly responsible for surfactant adsorption onto activated carbon.