"Spectroscopic Investigation of the Adsorption and Oxidation of Thiourea on Au(pc) and Au(111) in Acidic Media"

G. GARCÍA; J.L. RODRÍGUEZ; G.I. LACCONI; E. PASTOR*

LANGMUIR

American Chemical Society

Lugar: Washington DC.; Año: 2004 vol. 20 p. 8773 - 8780

0743-7463

In the present paper, a systematic electrochemical investigation on thiourea (TU) electrooxidation was developed on polycrystalline and (111) single-crystal gold electrodes in 0.1Mperchloric acid.Thecombination of cyclic voltammetry with in situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry techniques have allowed the nature of the species formed during the electroadsorption and electrooxidation of TU to be established. FTIRS experiments were performed inD2O to clean up the region of the H2O bending around 1600 cm-1. It was concluded that TU adsorbs tilted on the surface in the 0.05-0.40 VRHE potential range. A dual-path reaction mechanism was evidenced in the oxidation process. The first pathway takes place from adsorbed TU at E > 0.40 VRHE and implies the formation of [Au(I)-(TU)2]+, which is oxidized to NH2CN and S0 at E > 0.80 VRHE. In a following oxidation step at E > 1.20 V, N2, CO2, and HSO4-/SO42- were produced. The second parallel reaction occurs from TUin solution atE>0.50VRHE to form (TU)22+. All these species were characterized from the spectroscopic experiments. Similar results were obtained for both surfaces.