In-situ spectroscopic study of surfactant adsorption onto hematite from binary mixtures and the effect of inorganic ions

Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy has proven to be a powerful tool for surfactant adsorption studies. In many practical applications, surfactant mixtures and waters with different chemistry are employed, which significantly complicates adsorption studies. In this work, we investigate the effect of calcium and carbonate ions, frequently found in natural waters, on the co-adsorption of sodium dodecylbenzenesulfonate (SDBS) and a non-ionic primary alcohol ethoxylate (NEODOL 25-7) onto hematite at pH 8 and 10.5 using ATR-FTIR spectroscopy. Adsorption of SDBS was affected by pH and the presence of inorganic ions to a greater extent than the adsorption of NEODOL 25-7. A larger amount of SDBS was adsorbed at pH 8 than at pH 10.5 in all the experiments. The effect of co-adsorbing ions on the amount of SDBS adsorbed was significant only at pH 10.5 and not at pH 8. Calcium ions promoted adsorption of SBDS onto hematite, whereas addition of carbonate decreased the amount of SDBS adsorbed. In the presence of both calcium and carbonate ions, calcium carbonate precipitate was formed on the hematite surface, promoting accumulation of NEODOL 25-7 at the surface. NEODOL 25-7 was found to have a strong effect on the hydrophilicity of the hematite film when adsorbed in combination with SDBS. A more hydrophilic surface was obtained upon adsorption of the surfactants in the presence of sodium chloride, film dispersion occurred in the presence of calcium chloride, and a less hydrophilic surface was obtained in the presence of both calcium chloride and sodium carbonate. Copyright (C) 2014 John Wiley & Sons, Ltd.