Adsorption of potassium O,O′-Di(para-fluorophenyl) dithiophosphate on gold, silver, and copper

Gold, silver, and copper substrates were immersed in aqueous solutions of a simulant mineral flotation agent, potassium O,O'-di(para-fluorophenyl) dithiophosphate. The adsorbed molecules on gold were studied in detail with infrared reflection-absorption spectroscopy (IRAS), X-ray photoelectron spectroscopy(XPS), and ellipsometry. The most significant peaks in the IRAS spectra were assigned to the appropriate molecular vibrations and their relative intensities were compared with those found in simulated spectra derived from the isotropic optical constants of corresponding metal salts to deduce the binding and orientation. Moreover, intensity ratios of XPS signals were compared at different takeoff angles to reveal the depth distribution of atoms in the dithiophosphate layers. The following modes of adsorption were deduced: The adsorption on gold takes place by the formation of bonds involving the two sulfur atoms of the flotation agent (bridging coordination), regardless of immersion time and solution concentration. A thin and less organized layer is formed at low exposures. Longer adsorption times with more concentrated solutions give a more dense molecular packing and vertical orientation of the molecules on the surface. Adsorption on silver and copper was studied by IRAS. The adsorption proceeded via a dissolution-precipitation mechanism that manifests itself by less pronounced orientation effects. The intensities of the silver and copper IRAS spectra after long immersion times in concentrated solutions also show the formation of multilayers with some persisting long-range molecular ordering.