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Electrochemically Formed TiO2 Nanotube Arrays Site Selectively Decorated with Porous Au Particles By a Controlled Dewetting-Dealloying Approach - a Platform for Efficient Photocatalytic H2 Evolution

Wednesday, 1 June 2016
Exhibit Hall H (San Diego Convention Center)
N. T. Nguyen, M. Altomare (University of Erlangen-Nuremberg), and P. Schmuki (University of Erlangen-Nuremberg (FAU), King Abdulaziz University)
In the last decades TiO2 has received large attention due to its ability to “photocatalytically” split H2O into H2 and O2. Under “open-circuit” conditions, noble metal-modified (mainly Pt, Au or Pd) TiO2 is needed for H2 photo-generation.1 Not only the presence but also the size, amount and distribution of the noble metal particles affect the photocatalytic efficiency of TiO2.2,3

In this contribution we show that a most effective way to control the size and distribution of co-catalytic nanoparticles deposited on ordered TiO2 nanotube arrays is a controlled sputter-dewetting process.4

For this, we first grow electrochemically highly-ordered arrays of short aspect-ratio TiO2 nanotube in a o-H3PO4/HF electrolyte.5 The tubes growth is based on a simple anodization of a Ti metal substrate in self-ordering electrochemical conditions, and the morphology of the formed tubular oxide structures can be simply adjusted by the experimental conditions. These arrays of TiO2 nanotubes are coated with sputtered Au and Ag films, and a following controlled thermal treatment is carried out that leads at the same time to Au-Ag alloying and thermal dewetting of the conformal metallic film, that is, the sputtered metals are converted into an array of orderly distributed alloyed Au-Ag nanoparticles.

By adjusting the sputtering conditions, we are able to selectively deposit the Au-Ag nanoparticles at the rim and/or within the cavity of the TiO2 nanotubes. Subsequently, we perform a dealloying process, consisting in the selective chemical dissolution of Ag in a HNO3 solution, this leaving behind nanoporous Au particles on/into the tubes. Compared to tubes decorated by conventional approaches, remarkably enhanced photocatalytic H2 production is obtained upon porousification of the embedded Au nanoparticles. These porous Au/TiO2 nanotube structures show a remarkable photocatalytic enhancement particularly when the Au porous particles are selectively formed at the rims of the tubes (“crown” position).

[1] K. Lee, A. Mazare, P. Schmuki, Chem. Rev. 2014, 114, 9385–9454.

[2] N. T. Nguyen, J. Yoo, M. Altomare, P. Schmuki, Chem. Commun. 2014, 50, 9653–9656.

[3] N. T. Nguyen, M. Altomare, J. E. Yoo, N. Taccardi, P. Schmuki, Adv. Energy Mater. 2015, doi: 10.1002/aenm.201501926.

[4] N. T. Nguyen, M. Altomare, J. Yoo, P. Schmuki, Adv. Mater. 2015, 27, 3208–3215.

[5] J. E. Yoo, K. Lee, M. Altomare, E. Selli, P. Schmuki, Angew. Chem. Int. Ed. 2013, 52, 7514–7517.