XAS and XPS examination of the Au-S nanostructures produced via the reduction of aqueous gold(III) by sulfide ions

The S L- and Au L3-edge X-ray absorption fine structure and X-ray photoelectron spectra of nanoscale Au-S products formed via the reduction of aqueous HAuCl4 by sulfide ions and immobilized onto graphite have been acquired. The TEY XANES and XPS spectra implied the formation of predominant polysulfide species and metallic gold, while the transmission spectra showed Au-S bonding, the share of which increased with increasing molar Na2S/HAuCl4 ratio in the reaction solution. The Au-S distances derived from EXAFS analysis changes from 2.31 Å to 2.325 Å with the concentration of sodium sulfide in solution, being longer than that for cuprite-type crystalline Au2S (2.174 Å). It has been concluded from all the evidence that the surface of gold sulfide decomposes in air and in ultra-high vacuum even before X-ray irradiation.