Quantitative SHINERS Analysis of Temporal Changes in the Passive Layer at a Gold Electrode Surface in a Thiosulfate Solution

Abstract

Shell-isolated gold nanoparticles (SHINs) were employed to record shell-isolated nanoparticle-enhanced Raman spectra (SHINERS) of a passive layer formed at a gold surface during gold leaching from thiosulfate solutions. The (3-aminopropyl)triethoxysilane (APTES) and a sodium silicate solution were used to coat gold nanoparticles with a protective silica layer. This protective silica layer prevented interactions between the thiosulfate electrolyte and the gold core of the SHINs when the SHINs-modified gold electrode was immersed into the thiosulfate lixiviant. The SHINERS spectra of the passive layer, formed from thiosulfate decomposition, contained bands indicative of hydrolyzed APTES. We have demonstrated how to exploit the presence of these APTES bands as an internal standard to compensate for fluctuations of the surface enhancement of the electric field of the photon. We have also developed a procedure that allows for removal of the interfering APTES bands from the SHINERS spectra. These methodological advancements have enabled us to identify the species forming the passive layer and to determine that the formation of elemental sulfur, cyclo-S8, and polymeric sulfur chains is responsible for inhibition of gold dissolution in oxygen rich thiosulfate solutions.

Shell-isolated nanoparticle-enhanced Raman spectroscopy characterization of oxide ores during thiosulfate-mediated gold leaching

“…The appearance of bands in Fig. associated with metal sulfides and polysulfide chains suggests an increase in the quantity of these species at longer immersion times . These observations suggest that thiosulfate decomposition may follow the previously proposed mechanisms [Eqns and ] .…”

“…The sequentially acquired SHINERS spectra of the untreated and POX‐treated ore samples were recorded directly after exposure to the 0.10 M Na 2 S 2 O 3 electrolyte solution (pH = 10.0) and plotted in Figs (A) and (B) respectively. All observed peak positions and tentative assignments are summarized in Table . At early exposure to the thiosulfate electrolyte, two distinct narrow bands can be seen in Fig.…”

“…Unfortunately, the thin noble metal films or nanoparticles are unstable in thiosulfate electrolytes. Therefore SHINs, which are AuNPs encapsulated in an inert SiO 2 layer, provide the surface enhancement of the electric field of the photon and are ideally suited for characterizing the solid–liquid interface of oxide ores exposed to a thiosulfate electrolyte. In this study, we will demonstrate that SHINERS is able to provide information about differences in the composition of the passive layer when the untreated and POX‐treated oxide ore samples are immersed into a thiosulfate solution.…”

The effect of tetrathionate on the anodic process of gold thiosulfate leaching

“…S 3 O2− 4 and S 4 O2− 4, as the thiosulfate oxidation products, might also exist on the passive layer. 18 From the above findings, it can be said that the polythionates may not be observed on a gold surface during the passive process, but they do exist in the leaching solution in the form of decomposition products of thiosulfate. The polythionates were not observed on the gold surface after a prolonged leaching time.…”

Shell‐Isolated Nanoparticle‐Enhanced Raman Spectroscopy at Single‐Crystal Electrode Surfaces

“…The SERS-active Au NPs core of SHINs act as "signal amplifi ers" which can increase the Raman signals of probe molecules around or adsorbed on the target surface. [75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94] Notably, SHINERS technique employs shell-isolated mode which is different from contact mode and non-contact mode. [ 75 ] As a result, this technique can provide the original information about the target systems.…”