Unravelling the structural properties of mixed-valence α- and β-AuSe nanostructures using XRD, TEM and XPS

Colloidal and Deposited Products of the Interaction of Tetrachloroauric Acid with Hydrogen Selenide and Hydrogen Sulfide in Aqueous Solutions

“…The crystal structures of αand β-AuSe are well understood [30][31][32], but their electronic structure, particularly, the oxidation state of gold is a matter of dispute. The X-ray photoelectron Au 4f and valence band spectra (Figure 8) imply only one form of Au + and Se 2− both in linear and plain-square coordination of Au with Se (see also [42]). These findings agree with the results of quantum chemical calculations [37] and X-ray absorption spectra [36], but contradict 197 Au Mössbauer spectra [35], in which two types of Au atoms have been found both in α-AuSe and β-AuSe.…”

“…The Au 4f 7/2 peaks at 84.0-84.4 eV reported for gold-gold selenide [39][40][41], gold-CdSe [44,45]), adlayers of Se or alkyl selenides at Au [45][46][47][48][49]59], etc., originate from Au 0 surfaces but not AuSe phases. In nanostructured AuSe with admixture of Au [42], the values of 83.7 eV and 84.9 eV have been found, along with Se 3d 5/2 line at 54.5 eV, and ascribed to Au 0 and Au + , respectively; nevertheless, the authors assert the mixed valence state of gold (Au + Au 3+ Se 2 ). The BEs from 84.2 eV to 84.7 eV attributed to Au + in a series Ag-Au sulfides, selenides and sulfoselenides increase with decreasing content of Ag and the transfer of electron density from Ag to Au atoms [60,61].…”

“…The findings, which seemingly disagree with an excess of chalcogens found with EDS and also with a higher volatility of sulfur as compared with selenium, can be rationalized in terms of surface decomposition of gold chalcogenides, and different lateral resolution and probing depths of the techniques. The assignment of the Au 4f components is not straightforward, particularly, since AuSe contains two sorts of Au atoms, the oxidation state of which is a matter of dispute [35][36][37][38][39][40][41][42][43][44][45]. The Au 4f 7/2 peaks at 84.0-84.4 eV reported for gold-gold selenide [39][40][41], gold-CdSe [44,45]), adlayers of Se or alkyl selenides at Au [45][46][47][48][49]59], etc., originate from Au 0 surfaces but not AuSe phases.…”

“…It is known from chemistry textbooks (for example [38]) that direct interaction between aqueous gold complexes and selenide ions results in precipitation of unstable gold selenides with unclear compositions. Preparation of nanoscale materials containing gold selenide have been described in a few publications [17,[39][40][41][42][43][44][45]. Nath and co-workers [39] have synthesized "AuSe nanoalloys" via fusion of elemental Au and Se nanoparticles in a micellar solution, typically with an excess of Au NPs.…”

“…Prokeš et al [40] have used mixed dispersions of gold nanoparticles and elemental selenium, or Se powder suspended in HAuCl 4 solutions in various proportions as precursors for laser ablation, and detected in gas phase, by using mass-spectrometry, numerous gold-selenide nanoclusters Au m Se n leaning to compositions with Au/Se = 2 and Au/Se = 1. Machogo et al [42] have recently reported the preparation of AuSe nanostructures mixed with metallic nanogold and unreacted Se by the reaction of HAuCl 3 ·3H 2 O with elemental Se in oleylamine. It has been found in several studies aimed at synthesis of hybrid nanostructures that gold commonly deposits onto metal selenide nanoparticles in elemental form [43][44][45].…”