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Contribution Poster

Budker INP - 2nd and 3rd floors

A study of deposition of nanoscale intermediary Au-S species on oxide supports from aqueous solution using XAFS and TEM


  • Dr. Anton KARACHAROV

Primary authors



Nanoscale products deposited on oxide supports at room temperature from 0.1 mM tetrachloroaurate aqueous solutions and colloidal solutions (sols) of Au0 and gold sulfide nanoparticles, which were prepared beforehand by the reduction of the Au(III) complexes with sodium sulfide, were studied using total electron yield X-ray absorption near edge structure spectroscopy (TEY XANES), extended X-ray absorption fine structure spectroscopy (EXAFS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). It was found, that intermediary species of the sulfide reduction (Na2S/HAuCl4 = 3) was deposited on metal oxides as disordered Au2S, the surface of which tends to decompose yielding Au0NP’s with sulfur adlayer. This conclusion is supported by EXAFS, which shows that in case of gold deposited onto α-Fe2O3 in similar conditions, the average distance Au-S of the first coordination sphere was 2,32 Å, and a coordination number was equal to 1.1, i.e. gold was presented in a form disordered Au2S. According to TEY XANES and XPS data, the significant reduction or sulphidization of metal oxides surfaces are not occur, excepting CuO, onto which surface a Cu(I) sulfide was formed. For freshly prepared solution with the Na2S/HAuCl4 ratio of 3, a linear correlation between the quantity of gold deposited and isoelectric point of the oxide surface was found implying that intermediates bear a negative charge. The quantity of gold deposited from the intermediates solution of the citrate reduction of chloroaurate is lower, than from the final citrate sols and sulfidic sols, and high relative concentrations of oxidized forms of gold remain on substrates. Several metal oxides were decorated using the intermediates prepared with Na2S/HAuCl4 = 3. The TEM images show mainly Au0 NP’s in the range 3-5 nm, excepting CuO where ≈10 nm NP’s were observed.