Modulation of the electron transfer processes in noble metal/ZnO nanocomposites. Enhancement of UV activity of ZnO and plasmonic photocatalysis.

AGUIRRE, MATIAS EZEQUIEL

Sarasota

Conferencia; 27th Winter I-APS Conference; 2018

Interamerican Photochemical Society

Modulation of the electron transfer processes in noble metal/ZnO nanocomposites. Enhancement UV activity of ZnO and plasmonic photocatalysis.Matias E. AguirreInstituto de Investigaciones Físicas de Mar del Plata (IFIMAR)-Departamento de Química, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata-CONICET, Funes 3350, (7600) Mar del Plata, Prov. de Buenos Aires, Argentina. meaguirre@mdp.edu.arZinc oxide (ZnO) is an interesting broadband semiconductor of low cost and toxicity, with size-tunable optical properties. Its high stability in neutral and alkaline conditions has motivated its use in environmental remediation or industrial processes. The coupling of ZnO with noble metals can be exploited to modulate the harvesting, emission, and concentration of electromagnetic radiation. In this context, the recent advances in the design of core@shell nanocomposites (Ag@ZnO) for the enhancement the photocatalytic activity of ZnO in the UV region will be briefly commented, and the interest will be focused on the possibility of extending the semiconductor oxide response to the visible region of the electromagnetic spectrum, where it is not active. This phenomenon, reported for the first time by Tatsuma et al, is now known in the literature as Plasmonic Photocatalysis and can be defined as the set of processes that occur from the selective excitation of a metal with plasmonic characteristics (nanometric regime). Between the different processes that can be triggered by plasmon excitation of the metal, the formation (and transfer) of charge carriers is of particular interest, since it allows the occurrence of photoinduced redox reactions by visible radiation. In metal-semiconductor nanostructures, charge separation following plasmon excitation may be favored due to the injection of electrons into the conduction band of the semiconductor, however the existence of this phenomena has not been directly proved until recently. Here we will discuss the photoinduced changes in the oxidation states of a molecular probe 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl, TEMPOL (I), and its hydroxylamine, TEMPOL-H (II). We provide direct evidence that (I) and (II) can be interconverted by selective UV irradiation of the semiconductor and the metal in the visible region. The transfer of electrons in the Au to ZnO direction, after selective irradiation of the nanostructures in the visible region, is confirmed by direct observation of conduction band electrons in ZnO by EPR spectroscopy, under anaerobic conditions. Thus, we definitively probe that by modulating the excitation wavelength the electron flow direction can be switched, which is interesting for the development of logical devices.Finally, the influence of the morphology of nanostructures and solvent in the plasmonic efficiency will be discussed.REFERENCES Aguirre, M. E.; Municoy, S.; Grela, M. A.; Colussi A. J. Phys. Chem. Chem. Phys. 2017, 19, 4494-4499. Aguirre, M. E.; Rodríguez, H. B., San Román, E.; Feldhoff, A.; Grela, M. A. J. Phys. Chem. C 2011, 115, 24967?24974. Tian, Y.; Tatsuma, T. J. Am. Chem. Soc. 2005, 127, 7632-7637. Zhang, X.; Chen, Y. L.; Liu, R.-S.; Din Ping Tsai, D. P. Rep. Prog. Phys. 2013, 76, 046401. Aguirre, M. E., Custo, G., Goes, M. S., Bueno, P. R., Zampieri, G., Grela, M. A. J. Phys. Chem. C 2014, 118, 2018-2027. Aguirre, M. E., Armanelli, A., Perelstein, G., Feldhoff, A., Tolley, A. J., Grela, M. A. Nanoscale 2015, 7, 6667-6674.