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) dit hiophosphate. The adsorbed molecules on gold were studied in detail with in frared reflection-absorption spectroscopy (IRAS), X-ray photoelectron spect roscopy(XPS), and ellipsometry. The most significant peaks in the IRAS spec tra were assigned to the appropriate molecular vibrations and their relativ e intensities were compared with those found in simulated spectra derived f rom 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 a toms in the dithiophosphate layers. The following modes of adsorption were deduced: The adsorption on gold takes place by the formation of bonds invol ving the two sulfur atoms of the flotation agent (bridging coordination), r egardless of immersion time and solution concentration. A thin and less org anized layer is formed at low exposures. Longer adsorption times with more concentrated solutions give a more dense molecular packing and vertical ori entation of the molecules on the surface. Adsorption on silver and copper w as studied by IRAS. The adsorption proceeded via a dissolution-precipitatio n mechanism that manifests itself by less pronounced orientation effects. T he intensities of the silver and copper IRAS spectra after long immersion t imes in concentrated solutions also show the formation of multilayers with some persisting long-range molecular ordering.