Synthesis and comparative photocatalytic activity of Pt/WO 3 and Au/WO 3 nanocomposites under sunlight-type excitation M. Qamar a, * , Z.H. Yamani a, b , M.A. Gondal a, b , K. Alhooshani a, c a Center of Excellence in Nanotechnology, King Fahd University of Petroleum and Minerals, KFUPM Box 741, Dhahran 31261, Saudi Arabia b Physics Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia c Chemistry Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia article info Article history: Received 18 April 2011 Received in revised form 16 June 2011 Accepted 5 July 2011 Available online 12 July 2011 Keywords: Photocatalysis WO 3 Platinum Gold Nanocomposite abstract The article deals with the synthesis of highly active visible-light-driven nanocomposite for the decon- tamination of water hazards under sunlight-type excitation. The surface of visible-light-active nano- structured photocatalyst tungsten oxide (WO 3 ) was modified with noble metals, such as platinum (Pt) and gold (Au) nanoparticles, and the resulting photocatalytic activity of the nanocomposites was investigated by studying the removal of Methyl Orange and 2,4-Dichlorophenoxyacetic acid (2,4-D) under sunlight-type excitation. The study revealed that the deposited noble metals are not always favorable for the enhancement of photocatalytic response of catalysts; the activity of WO 3 was enhanced manyfold (w8 times) by depositing an optimum amount of Pt nanoparticles after certain photo- deposition time whereas the presence of Au nanoparticles onto the WO 3 surface, under identical experimental conditions, affected the removal process negatively. The variation in the photocatalytic activity of nanocomposites was attributed to the size of the deposited metals; Pt nanoparticles were uniformly dispersed with narrow size distribution (2e4 nm) while the size distribution of Au nano- particles was found to be 10e15 nm for similar preparation conditions. The effects of critical parameters, such as metal deposition time and metal contents, on the photocatalytic activity of WO 3 were investi- gated. Furthermore, Pt/WO 3 nanocomposites showed good stability and recyclability under the condi- tions studied. Ó 2011 Elsevier Masson SAS. All rights reserved. 1. Introduction Water is one of the basic resources for the existence of life on earth. The availability of clean water is a major problem nowadays, and is expected to increase in the future due to the heavy global industrialization and increase in human population. Among many processes being proposed and/or developed for water purification, semiconductor-mediated photocatalytic processing has received considerable attention. It is now well-established that photo- catalysis is an efficient method to decompose the undesirable pollutants (dyes, pesticides, heavy metals etc.) and inactivate pathogens present in water/wastewater under solar light or illu- minated light source [1e5]. Yet, photocatalytic processes using semiconductors need to overcome the limitations in achieving higher photoconversion efficiencies. The fundamentals of hetero- geneous photocatalytic oxidation processes have been discussed extensively in the literature [6e11]. Briefly, when a photocatalyst absorbs a photon of energy equal to or greater than its band gap, an electron may be promoted from the valence band to the conduction band (e  cb) leaving behind an electron vacancy or “hole” in the valence band (h þ vb). If the charge separation is maintained, the electron and hole may migrate to the catalyst’s surface where they participate in redox and oxidation reactions with adsorbed species. Due to its unique properties such as chemical, thermal and photo-stability, non-toxicity, high activity and relatively low cost, TiO 2 is currently the best known and most widely researched photocatalytic material for the remediation of environmental hazards [12e14]. However, low absorption in UV region (3e5%) and high recombination of electron-hole pairs (w90%) are the over- riding limitations of the photocatalysis involving TiO 2 [15]. Considerable attention therefore has been given to the develop- ment of visible-light-driven photocatalysts with most research focused on achieving efficient decomposition of environmental organic contaminants with the help of solar or artificial light [16e21]. Attempts have been made to extend the absorption edge of TiO 2 from ultraviolet to visible range by incorporating some * Corresponding author. Tel.: þ966 38607775; fax: þ966 38607264. E-mail address: qamar@kfupm.edu.sa (M. Qamar). Contents lists available at ScienceDirect Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie 1293-2558/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2011.07.002 Solid State Sciences 13 (2011) 1748e1754