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 t he ionic surfactants. sodium dodecylsulfate (SDS) and cetyltrimethylammoniu m bromide (CTAB), from aqueous solution to metal oxide particle films. Thin porous metal oxide particle films were prepared by drying of aqueous collo idal 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 pri marily via electrostatic and hydrogen bonding interactions between the sulf ate headgroup and the metal oxide surfaces. The adsorption of CTAB to negat ively charged TiO2, and Ta2O5 was observed. The pH dependence of CTAB adsor ption to TiO2, indicated that both electrostatic and hydrophobic interactio ns are important. Langmuir adsorption constants from isotherm data were sim ilar for adsorption of CTAB on TiO2, at pH = 6.3 and at pH = 11.0 indicatin g that charge effects are not dominant in this pH range. Use of a single in ternal reflection prism allowed the displacement of interfacial water by su rfactant adsorption to be clearly discerned in the spectra, (C) 2000 Elsevi er Science B.V. All rights reserved.