X-ray Photoelectron Spectroscopy (XPS) Study of the Products Formed on Sulfide Minerals Upon the Interaction with Aqueous Platinum (IV) Chloride Complexes

Abstract

The interaction of aqueous solutions bearing platinum-group elements (PGEs) with sulfides is important for understanding the formation and weathering of PGE ore deposits, mineral processing, and synthesis of nanomaterials. Here, the surface species formed upon the contact of the main sulfide minerals (pyrite, pyrrhotite, galena, chalcopyrite and valleriite) with the solutions of H 2 PtCl 6 (pH 1.5, 20 • C) have been studied using X-ray photoelectron spectroscopy (XPS). Uptake of Pt increased gradually with increasing interaction time, and depended, as well as the composition of immobilized products, on the mineral nature and the state of its surface, e.g., the chemical pre-treatment. The highest rate of Pt deposition was observed on galena and valleriite and the lowest on pyrite and pyrrhotite. The preliminary moderate oxidation of pyrrhotite promoted Pt deposition, which, however, was hindered under harsh reaction conditions. The pre-oxidation of pyrite in all cases resulted in a decrease of the Pt deposition. Initially, Pt(IV) chloride complexes adsorb onto the mineral surface, and then the reduction of Pt(IV) to Pt(II) and substitution of chloride ions with sulfide groups occur forming sulfides of Pt(II) and then, Pt(IV). The reduction of Pt species to the metallic state was observed at valleriite after 24 h, probably due the negative charge of the sulfide nanolayers of this sulfide-hydroxide composite mineral.

Platinum single-atom catalyst coupled with transition metal/metal oxide heterostructure for accelerating alkaline hydrogen evolution reaction

“…Specifically, the Pt SA -NiO shows the largest positive shift in Pt 4 f spectrum, suggesting the maximum electron loss of Pt species 44 , 45 . Besides, the fitting curve of Pt XPS spectrums display Pt(IV) species in the samples, which derives from the adsorbed PtCl 6 2 − ions on the surface of the sample 46 , 47 . Further, the electronic state and atomic environment of Pt atoms in NiO/Ni, NiO, and Ni supports are further verified by performing X-ray absorption fine structure measurements.…”

Tailoring Water Dissociation Energy by Platinum Single-Atom Catalyst Coupled with Transition Metal/metal Oxide Heterostructure for Accelerating Alkaline Hydrogen Evolution Reaction

“…42,43 Besides, the fitting curve of Pt XPS spectrums display Pt(IV) species in the samples, which derives from the adsorbed PtCl6 2ions on the surface of the sample. 44,45 Further, the electronic state of Pt atoms in NiO/Ni, NiO, and Ni supports are further verified by performing X-ray absorption fine structure measurements. As shown in Figure 3b, the evolutions of Pt L3-edge X-ray absorption near edge structure (XANES) spectra with different supports are distinguished, in which the intensity of white-line peaks corresponds to the transfer of the Pt 2p3/2 core-electron to 5d states, and thus is used as an indicator of Pt 5d-band occupancy.…”

Photocatalytic Activity of Cellulose Acetate Nanoceria/Pt Hybrid Mats Driven by Visible Light Irradiation

“…In all the other cases, after thermal treatment, the signal attributed to the Ce 4+ –O lattice disappears, and the O1s peak located in the 532.54–532.70 eV range (depending on the sample, Supplementary Figure S11d–f ) can be attributed to the overall oxygen groups of the cellulosic membrane [ 35 , 36 ], as well as to the oxygen vacancies possibly due to the prevalent presence of Ce 3+ on the surface of the mats. Concerning the CA/CeNPs/Pt mats, the Pt 4f spectra ( Figure 5 e,f) present the typical binding energies of Pt species [ 37 ] in the Pt 4f region due to the presence of multiple oxidation states. In particular, the signals of Pt 4f 5/2 and 4f 7/2 were deconvoluted into two sets of spin-orbit doublets, indicating the presence of Pt in two forms, the Pt 0 and Pt 2+ on the surface of the mats, the latter being present as PtO or Pt(OH) 2 [ 30 ].…”