The silver nanoparticles/TiO2 interface: a combined electrochemical and theoretical investigation

A modified electrode, made by silver nanoparticles covered with a thin layer of titanium dioxide (anatase polymorph) was prepared and electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Previously synthesized silver nanoparticles (mean diameter 10 ± 2 nm) were immobilized on an inert support (aminosiloxane-functionalized fluorine-doped tin oxide) and subsequently covered with a 100 nm-thick layer of titania using our previously reported methodology [1]. Electrochemical studies showed a pronounced electrocatalytic effect and an increase in the current intensity of the silver oxidation peak in comparison with the results reported in the literature for uncovered silver nanoparticles [2-4]. Moreover, the resulting composite showed a strong UV light response: complete restoration of the silver oxidation current peak was observed when the composite was irradiated after performing a voltammetric scan, thanks to the UV-assisted reduction of the passivating oxide layer. These results are explained by theoretical DFT calculations, performed using the VASP code [5-10]. Namely, an interface of silver on the (101) cut of anatase TiO2 was grown and characterized. A commensurate Ag structure was found, showing an interaction in the region of the junction between silver atoms and TiO2. The interaction was justified by the Ag-O distances and the atomic charges computed using a special code [11-13], which takes in input the outputs of VASP. The silver atoms close to the semiconductor gain a partially positive charge, while the oxygens of TiO2 host the negative ones. The charge transfer decreases with the distance from TiO2 and characterizes the metal-semiconductor junction. This theoretical picture allowed us to find a very good agreement between theory and experiment, shining light on a system of both great theoretical and applicative interest. REFERENCES [1] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst, (2015), 140, 1486 – 1494. [2] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc., (2010), 132, 70–72 [3] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B, (2005), 109, 1204-1209 [4] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C, (2008), 112, 17820–17827. [5] G. Kresse, J. Hafner, Phys. Rev. B: Condens. Matter, (1993), 47, 558−561. [6] G. Kresse, J. Furthmuller, Phys. Rev. B: Condens. Matter, (1996), 54, 11169−11186. [7] P.E. Blöchl, Phys. Rev. B: Condens. Matter, (1994), 50, 17953−17979. [8] G. Kresse, D. Joubert, Phys. Rev. B: Condens. Matter, (1999), 59, 1758−1775. [9] J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett., (1996), 77, 3865−3868. [10] G. Kresse, J. Hafner, Phys. Rev. B: Condens. Matter, (1994), 49, 14251−14269. [11] W. Tang, E. Sanville, G. Henkelman, J. Phys. Condens. Matter, (2009), 21, 084204. [12] E. Sanville, S. D. Kenny, R. Smith, G. Henkelman, J. Comp. Chem., (2007), 28, 899. [13] G. Henkelman, A. Arnaldsson, H. Jónsson, Comput. Mater. Sci., (2006), 36, 254.