An in situ infrared spectroscopic investigation of adsorption of sodium dodecylsulfate and of cetyltrimethylammonium bromide surfactants to TiO2, ZrO2, Al2O3, and Ta2O5 particle films from aqueous solutions

An in situ infrared spectroscopic study is described of the adsorption of the ionic surfactants. sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB), from aqueous solution to metal oxide particle films. Thin porous metal oxide particle films were prepared by drying of aqueous colloidal dispersions on single internal reflection ZnSe prisms. Analysis of the spectra of SDS in both aqueous solution and adsorbed to positively charged TiO2, ZrO2, Al2O3, and Ta2O5 surfaces indicates that adsorption occurs primarily via electrostatic and hydrogen bonding interactions between the sulfate headgroup and the metal oxide surfaces. The adsorption of CTAB to negatively charged TiO2, and Ta2O5 was observed. The pH dependence of CTAB adsorption to TiO2, indicated that both electrostatic and hydrophobic interactions are important. Langmuir adsorption constants from isotherm data were similar for adsorption of CTAB on TiO2, at pH = 6.3 and at pH = 11.0 indicating that charge effects are not dominant in this pH range. Use of a single internal reflection prism allowed the displacement of interfacial water by surfactant adsorption to be clearly discerned in the spectra, (C) 2000 Elsevier Science B.V. All rights reserved.