Hydrogen production over metal-loaded mesoporous-assembled SrTiO 3 nanocrystal photocatalysts: Effects of metal type and loading Tarawipa Puangpetch a , Thammanoon Sreethawong a,b, *, Sumaeth Chavadej a,b a The Petroleum and Petrochemical College, Chulalongkorn University, Soi Chula 12, Phyathai Road, Pathumwan, Bangkok 10330, Thailand b Center for Petroleum, Petrochemicals, and Advanced Materials, Chulalongkorn University, Bangkok 10330, Thailand article info Article history: Received 4 January 2010 Received in revised form 29 March 2010 Accepted 5 April 2010 Available online 6 May 2010 Keywords: Gold loading Strontium titanate Mesoporous assembly Solegel method Structure-directing surfactant Photocatalytic hydrogen production abstract Mesoporous-assembled SrTiO 3 photocatalysts with different loaded metal co-catalysts (Au, Pt, Ag, Ni, Ce, and Fe) synthesized by the single-step solegel method with the aid of a structure-directing surfactant were tested for the photocatalytic activity of hydrogen production from a methanol aqueous solution under both UV and visible light irradiation. The Au, Pt, Ag, and Ni loadings had a positive effect on the photocatalytic activity enhancement, whereas the Ce and Fe loadings did not. The best loaded metal was found to be Au due to its electrochemical properties compatible with the SrTiO 3 -based photocatalyst and its visible light harvesting enhancement. A 1 wt.% Au-loaded SrTiO 3 photocatalyst exhibited the highest photocatalytic hydrogen production activity with a hydrogen production rate of 337 and 200 mmol h 1 g cat 1 under UV and visible light irradiation, respectively. The hydrogen diffusivity from the liquid phase to the gas phase also signifi- cantly affected the photocatalytic hydrogen production efficiency. An increase in the hydrogen diffusability led to an increase in the photocatalytic hydrogen production efficiency. ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. 1. Introduction For hydrogen production from the photocatalytic water splitting reaction, the three main reasons for the low hydrogen production activity of most photocatalysts are the high recombination rate between the photo-generated elec- tron and hole [1], the fast backward reaction between hydrogen and oxygen into water [2e8], and the limited light harvesting ability of the photocatalysts themselves [3,9e11]. Hence, several research projects have focused on eliminating these obstacles and enhancing the visible light harvesting ability of the photocatalysts [12e20]. One interesting approach used for enhancement of the photocatalytic activity of hydrogen evolution by increasing the charge transfer to reduce the recombination rate is to load a metal catalyst, or co-catalyst. The loaded metal, or co-catalyst, can act as a charge transferring site and/or active site for the photo- catalytic reaction. It has been reported that the photocatalytic activity of TiO 2 can be remarkably enhanced by the loading of a small amount of a Pt co-catalyst [21e27]. The enhancement in the photocatalytic activity can be explained by the photo- electrochemical mechanism, in which the photo-generated * Corresponding author at: The Petroleum and Petrochemical College, Chulalongkorn University, Soi Chula 12, Phyathai Road, Pathumwan, Bangkok 10330, Thailand. Tel.: þ66 2 218 4144; fax: þ66 2 215 4459. E-mail address: thammanoon.s@chula.ac.th (T. Sreethawong). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 35 (2010) 6531 e6540 0360-3199/$ e see front matter ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2010.04.015