Chemical Engineering Journal 173 (2011) 667–675 Contents lists available at ScienceDirect Chemical Engineering Journal j ourna l ho mepage: www.elsevier.com/locate/cej Comparative investigation of hydrogen production over Ag-, Ni-, and Cu-loaded mesoporous-assembled TiO 2 –ZrO 2 mixed oxide nanocrystal photocatalysts Surakerk Onsuratoom a , Tarawipa Puangpetch b , Sumaeth Chavadej a,c,∗ a The Petroleum and Petrochemical College, Chulalongkorn University, Soi Chula 12, Phyathai Road, Pathumwan, Bangkok 10330, Thailand b Department of Chemical Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Nakhon Pathom 73000, Thailand c Center for Petroleum, Petrochemicals, and Advanced Materials, Chulalongkorn University, Bangkok 10330, Thailand a r t i c l e i n f o Article history: Received 13 April 2011 Received in revised form 4 July 2011 Accepted 4 August 2011 Keywords: Photocatalytic hydrogen production Sol–gel process Mesoporous assembly TiO2–ZrO2 mixed oxide Metal loading a b s t r a c t This work focused on the enhancement of photocatalytic hydrogen production activity under UV light irradiation of mesoporous-assembled 0.93TiO 2 –0.07ZrO 2 mixed oxide nanocrystal photocatalysts (having the TiO 2 -to-ZrO 2 molar ratio of 93:7) by non-precious metal (Ag, Ni, and Cu) loadings via a photochemical deposition method. The mesoporous-assembled 0.93TiO 2 –0.07ZrO 2 mixed oxide was synthesized by a sol–gel process with the aid of a structure-directing surfactant prior to the metal loadings. The prepared photocatalysts were characterized by N 2 adsorption–desorption, scanning elec- tron microscopy, transmission electron microscopy, X-ray energy dispersive analysis, X-ray diffraction, UV–visible spectroscopy, and H 2 chemisorption. The most efficient loaded metal was found to be Cu due to its suitable physical, chemical, and electrochemical properties with the 0.93TiO 2 –0.07ZrO 2 mixed oxide-based photocatalyst. The 0.15 wt.% Cu-loaded 0.93TiO 2 –0.07ZrO 2 mixed oxide photocata- lyst exhibited the highest photocatalytic hydrogen production activity with a hydrogen production rate of 12.8 cm 3 h -1 g cat -1 . © 2011 Elsevier B.V. All rights reserved. 1. Introduction Hydrogen is more increasingly considered to be an ideal source of future energy because clean, low-cost, and environmentally friendly production of hydrogen can be achieved with the aid of solar energy [1–4]. However, most of current hydrogen needs are served by steam reforming of methane, which is a non-renewable energy source, so the sustainable hydrogen production systems are of great importance in the near future [5–8]. Especially, hydrogen production from renewable energy source is promising process, e.g. via photocatalytic processes [9–13]. TiO 2 has been widely used as a photocatalyst for light-to-energy conversion and chem- ical transformations [14]; however, TiO 2 itself still exhibits low photocatalytic efficiency. Hence, the improvement of its photo- catalytic activity has been extensively investigated and found to be achieved by several techniques, such as doping of metals on its surface or in its structure, addition of electron donors (hole scavengers) to the reaction system, and establishment of suit- ∗ Corresponding author at: The Petroleum and Petrochemical College, Chula- longkorn University, Soi Chula 12, Phyathai Road, Pathumwan, Bangkok 10330, Thailand. Tel.: +66 2 218 4139; fax: +66 2 218 4139. E-mail address: sumaeth.c@chula.ac.th (S. Chavadej). able semiconductor–semiconductor mixed oxide [15–17]. These techniques enhance the charge carrier separation by reducing the probability of the charge carrier recombination. In addition, several research works have reported that the loading of some effective precious noble metals, especially Pt, Au, and Pd, on a semicon- ductor surface significantly improves the photocatalytic activity [18–23]; nevertheless, such metals are very costly in the viewpoint of practical use. More interestingly, effective non-precious transition metals, particularly Ag, Ni, and Cu, can also be employed for the photocat- alytic activity enhancement [24–29]. However, to our knowledge, these non-precious metals (Ag, Ni, and Cu) have received much less attention to be investigated for the photocatalytic hydrogen pro- duction as compared to the aforementioned precious noble metals, and their comparative investigation of loading on a specific base semiconductor photocatalyst for such a purpose has not yet been studied and reported. In our previous work [30], the mesoporous-assembled TiO 2 –ZrO 2 mixed oxide nanocrystal with the TiO 2 -to-ZrO 2 molar ratio of 93:7 (i.e. 0.93TiO 2 –0.07ZrO 2 ) synthesized by a sol–gel pro- cess with the aid of a structure-directing surfactant was found to exhibit an acceptably high photocatalytic hydrogen production activity, as compared to the synthesized pure mesoporous- assembled TiO 2 and commercial non-mesoporous-assembled TiO 2 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.08.016