Electron beam induced rapid crystallization of water splitting nanostructures
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Electron beam induced rapid crystallization of water splitting nanostructures Nitul S. Rajput1, Sang-Gook Kim2, Jeffrey B. Chou2, Jehad Abed1, Jaime Viegas1 and Mustapha Jouiad1 1 Masdar Institute of Science and Technology, Masdar City, Abu Dhabi, UAE 2 Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139, USA ABSTRACT Titanium dioxide (TiO2) loaded with gold (Au) as noble metal, acts as an efficient photocatalyst that has been extensively investigated for water splitting processes. In this paper, we report on the microstructure of atomic layer deposited titanium dioxide and the crystallinity modification of the material using energetic electron beam irradiation. A rapid high-energy electron beam induced crystallization of the nanostructures has been observed in-situ inside a High-Resolution Transmission Electron Microscope (HRTEM). The systematic crystallization of the nanomaterial occurring under the electron beam irradiation (300 KV) indicates the transformation of the near amorphous material into a mixture of two nuances of TiO2 polymorphs, namely rutile and anatase. We believe that this transformation will enhance the efficiency of water splitting process, as the mixed phases of rutile and anatase are known to possess better optical properties than the individual polymorphs of TiO2. This finding may be of particular interest in developing appropriate heat treatment methods for these nanostructures dedicated to water splitting to increase their efficiency. INTRODUCTION The energy solutions for the future suggest the realization and development of eco-friendly and economic energy sources. Many natural sources such as, solar energy, wind energy and biofuels have been used in order to reduce the carbon emission. In this regard, solar energy assisted water splitting and hydrogen production has shown a promising potential. In 1972, Fujishima and Honda showed that TiO2 could be a potential catalyst in water splitting process [1]. Since then, a large amount of studies have been performed on TiO2 and other equivalent photonic structures. TiO2 has a band gap of 3.2 eV, which falls in the UV region of the light spectrum. Thus, water splitting (WS) efficiency is limited within the UV region. However by adding localized surface plasmon resonance (LSPR) particles to the oxide material, the optical activity of the composite plasmonic-metal/semiconductor photocatalysts (MPhC) can be significantly enhanced [2, 3]. In the MPhC structures used in our studies, TiO2 acts as the WS catalyst and Au nanoparticles as the LSPR material. In this case, the WS activity fundamentally can depend on the (i) production rate of hot electrons in the Au part through plasmon resonance, (ii) the
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transport of the hot electrons produced in Au to the TiO2 material, and (iii) the degr
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