CONICET | Buscador de Institutos y Recursos Humanos

Hybrid nanostructures composed by noble metals and wide bandgap semi-conductors are interesting materials for molecular optoelectronics, energy conversion and catalysis. Here we present definitive evidence of the plasmon photoinduced electron transfer from Au to ZnO nanoparticles by direct detection of free conduction electrons by EPR spectroscopy. [1] Figure 1 compares the EPR spectra of pure ZnO nanoparticles suspended in ethylene glycol (a), and that of Au/ZnO nanostructures before, (b), and during irradiation at wavelengths longer than 435 nm, (c). The synthesized Au/ZnO nanostructures in the dark, showed a small feature at g = 1.9655, which is assigned to the presence of free electrons in the conduction band. Its origin its attributted to the charge transfer process taking place during the synthesis of the nanostructures to equilibrate their Fermi energy levels. Curve c) shows that visible irradiation (mayor a 435 nm) of the sample leads to a sudden outstanding increase of the singlet at g = 1.9623; the shift to higher fields with respect to the dark value indicates that electrons preferentially reside in larger sized particles which favour electron delocalization [1,2]. Also, by analyzing the redox transformations between the oxidation states of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl, tempol (I), the hydroxylamine (II) and its oxoammonium cation (III), we showed that (I) and (II) can be interconverted by selective irradiation of the semiconductor (UV) and the plasmon band (in the visible region). The results indicate that by modulating the excitation wavelength the electron flow direction can be switched, a fact that may be exploited for the development of logical devices.

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