Infrared and X-ray photoelectron spectroscopy studies on the adsorption of gold cyanide on activated carbon

The understanding of the adsorption of gold cyanide on activated carbon has greatly benefited from recent investigations using Mössbauer, X-ray photoelectron (XPS) and infrared (IR) spectroscopy. While Mössbauer spectroscopy produced definitive results, XPS and IR spectroscopy have not achieved the same irrefutable success. XPS binding energies differed from one study to another because of uncertainties in calibration. IR studies, on the other hand, are difficult because of the opacity of activated carbon. In addition, no systematic analysis of IR results has been offered. XPS and IR spectroscopy were, therefore, performed on KAu(CN)2 and Au(CN)2− adsorbed on activated carbon. XPS results in the literature, after corrections, and from this study agree remarkably well with each other. The IR data were analysed in terms of the Hookeʹs law approximation of absorption frequencies and a molecular orbital model of the cyanide radical. In combination, the XPS and IR results are consistent with the adsorption of gold cyanide by a weak donation of π-electrons from activated carbon to gold. The adsorbed species is most likely the unpaired dicyano complex, which does not undergo any chemical change other than the adsorption interaction itself. No evidence was found to support the ion-pair adsorption model. To the contrary, the model becomes self contradicting when scrutinised with the IR and XPS results.