Surfactant Adsorption by Zeolite: Hemimicelle Formation and Cooperative Adsorption

Adsorption of cationic surfactants on zeolites was measured potentiometrically by use of surfactant cation selective electrode. The surfactants used were dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB). Analysis of the binding isotherms indicates non- or less cooperative nature in the surfactant binding by zeolite. This fact suggests a difficulty of aggregation of bound surfactant ions like hcmimicclIe. On the other hand, fluorescence probing study by use of pyrene (Py) clearly indicated a formation of hydrophobic microenvironment even at a very small amount of bound surfactant. Probing study by 1-pyrenylaldehyde (PyA), however, indicated a gradual growth of hydrophobic nature of the microenvironment. The latter fact is consistent with the inference from the binding isotherm. Pyrene absorbed on zeolite is inferred to induce clustering of surfactant ions.