CHEMICAL ENGINEERING TRANSACTIONS VOL. 39, 2014 A publication of The Italian Association of Chemical Engineering www.aidic.it/cet Guest Editors: Petar Sabev Varbanov, Jiří Jaromír Klemeš, Peng Yen Liew, Jun Yow Yong Copyright © 2014, AIDIC Servizi S.r.l., ISBN 978-88-95608-30-3; ISSN 2283-9216 DOI: 10.3303/CET1439272 Please cite this article as: Ampelli C., Genovese C., Lanzafame P., Perathoner S., Centi G., 2014, A sustainable production of H2 by water splitting and photo-reforming of organic wastes on Au/TiO2 nanotube arrays, Chemical Engineering Transactions, 39, 1627-1632 DOI:10.3303/CET1439272 1627 A Sustainable Production of H 2 by Water Splitting and Photo-Reforming of Organic Wastes on Au/TiO 2 Nanotube Arrays Claudio Ampelli*, Chiara Genovese, Paola Lanzafame, Siglinda Perathoner, Gabriele Centi Department of Electronic Engineering, Chemistry and Industrial Engineering, University of Messina Viale F. Stagno D’Alcontres 31 - 98166 Messina, Italy ampellic@unime.it We report here on the sustainable production of hydrogen by the use of nano-ordered TiO2 arrays doped with gold nanoparticles (Au NPs). The presence of a nano-architecture in TiO2 substrate may strongly improve the ability to disperse the Au NPs on its surface, which act as electron-attractive centres for the reduction of protons. We prepared the TiO2 nanotube arrays by controlled anodic oxidation starting from Ti foils and deposited the Au NPs by pre-preparing gold colloidal solutions. The samples were characterized by Transmission Electron Microscopy (TEM), UV-Visible Diffusive Reflectance Spectroscopy, Cyclic Voltammetry and Chronoamperometry. Then, they were tested within our homemade photo- electrochemical (PEC) reactors in water photo-splitting, as well as in photo-dehydrogenation of ethanol for H2 production. A solar simulator was used to evaluate their photo-responses in different absorption regions (ultraviolet or visible part). Results evidenced that smaller Au NPs strongly enhanced titania performances under visible light irradiation, opening the route of a feasible implementation of the PEC devices in the energy recovery from organic waste solutions (i.e. from biomass processing) that are too dilute to be processed by conventional routes. 1. Introduction Solar energy is undoubtedly the more promising alternative option to fossil fuels for the future global economy. The amount of sunlight striking continuously the Earth’s surface can be considered as an abundant, largely untapped energy resource (Genovese et al., 2013a) and research progress has evidenced that direct conversion of solar to chemical energy may be performed in an one-step process by water photo-electrolysis (process intensification). Unfortunately, the photo-active materials currently used to harvest sunlight and split water, are poorly efficient under visible illumination (Ampelli et al., 2011a). The more known example is titania (TiO2), a promising semi-conductor material but limited by its high band gap (~3.2 eV) which sets its light absorption within the ultraviolet region of the electromagnetic spectrum. Several attempts have been in literature to extend the cut-off wavelength of this catalyst, including doping the crystalline lattice with hetero-atoms or decorating its surface with metal nanoparticles (NPs), but only slight improvements have been resulted (Passalacqua et al., 2012). Among the other metals, Au represents a special case; though it is well known that Au NPs positively influence solar light harvesting of titania through surface plasmon resonance, the mechanism of interaction of the plasmons with the conduction band of titania has not unequivocally interpreted yet (Tian and Tatsuma, 2005). Contrasting explanations have been given to interpret visible light enhancement of Au NPs, but it is agreed that their size and dispersion, together with the titania morphology, are fundamental for obtaining good responses in terms of light absorption and photo-catalytic response. Recently, Notarianni et al. (2013) showed that concentration, size and geometry of Au NPs are key factors that directly influence the light absorption in organic solar cells. The correct choice of size, concentration and location of Au NPs resulted in an enhancement of the power conversion efficiencies. Min et al. (2009) observed that Au NPs supported on