Synchrotron XPS studies of collector adsorption and co-adsorption on gold and gold: silver alloy surfaces

Abstract

The adsorption and co-adsorption of two flotation collectors (sodium 2-mercaptobenzothiazole (MBT) and potassium di-isoamyl dithiophosphate (DTP) on gold and gold:silver alloy surfaces has been studied using synchrotron X-ray photoelectron spectroscopy. The use of synchrotron radiation (NSRRC, Taiwan) and a newly designed/built soft X-ray endstation (commissioned in Taiwan and now installed at the Australian Synchrotron) has enabled the collection of high signal-to-noise, high resolution spectra of the sulfur 2p peak for the adsorbed collectors. Both collectors were observed to adsorb on gold and gold:silver surfaces. Multiple S 2p doublets were observed in the photoemission spectra, in spite of the fact that the solution conditions and exposure times ensured (sub)monolayer (rather than multilayer) adsorption. MBT is seen to have two chemisorbed geometries when adsorbed on gold and only one when adsorbed on gold:silver substrates. The spectra also indicate that DTP may have two chemisorbed geometries (bidentate and monodentate), on both gold and gold:silver substrates. In addition, both surfaces were shown to co-adsorb the collectors, with some variation in the relative adsorbed amounts: MBT adsorbs more extensively than DTP from the solution mixture onto gold; the reverse is true for the gold:silver substrate.