Journal of Molecular Catalysis A: Chemical 366 (2013) 54–63 Contents lists available at SciVerse ScienceDirect Journal of Molecular Catalysis A: Chemical jou rn al h om epa ge: www.elsevier.com/locate/molcata Enhanced photocatalytic performance of WO 3 loaded Ag–ZnO for Acid Black 1 degradation by UV-A light B. Subash, B. Krishnakumar, M. Swaminathan, M. Shanthi ∗ Photocatalysis Laboratory, Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India a r t i c l e i n f o Article history: Received 8 May 2012 Received in revised form 7 September 2012 Accepted 9 September 2012 Available online 16 September 2012 Keywords: WO3 loaded Ag–ZnO Photocatalysis UV-A light Acid Black 1 Reusability a b s t r a c t The WO 3 loaded Ag–ZnO (WO 3 -Ag–ZnO) was successfully synthesized by solvothermal method. The catalyst was characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE- SEM) images, transmission electron microscope (TEM) images, energy dispersive spectra (EDS), diffuse reflectance spectra (DRS), photoluminescence spectra (PL), cyclic voltammetry (CV) and BET surface area measurements. The photocatalytic activity of WO 3 -Ag–ZnO was investigated for the degradation of Acid Black 1 (AB 1) in aqueous solution using UV-A light. WO 3 -Ag–ZnO is found to be more efficient than Ag–ZnO, WO 3 –ZnO, Ag–WO 3 , commercial ZnO, prepared (bare) ZnO, TiO 2 -P25 and TiO 2 (Merck) at pH 9 for the mineralization of AB 1. The effects of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photo mineralization of AB 1 have been analyzed. The mineralization of AB 1 has been confirmed by COD measurements. The catalyst is found to be reusable. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The absorption of sufficiently energetic UV-light by a wide band- gap semiconductor results in the creation of electrons and holes through a process of electronic excitation between the valence and conduction bands. Once created, these photogenerated charge car- riers are able to migrate to the surface of the semiconductor and undergo redox reactions with adsorbed molecules. Loading a cocat- alyst onto a semiconductor photocatalyst is required to lower the overvoltage for the hydrogen and oxygen evolution systems. The cocatalyst also suppresses the recombination of photogenerated charges in the photocatalyst by efficient removal of photoelec- trons from the charge generation sites, and provides the catalytic sites for the reduction of H + ion. The charge recombination is the main cause of decrease in efficiency, because some of the absorbed photoenergy is wasted as useless fluorescence light or heat. The use of heterogeneous photocatalysts in the degradation of envi- ronmental pollutants has attracted intensive attention during the past two decades [1–5]. Among various semiconductor photocata- lysts used for removal of toxic pollutants and sewage treatment, nano structured ZnO materials were extensively used owing to their high photosensitivity, stability, low cost and non-toxicity [6–9]. However, the photoexcited electrons and holes can also recom- bine to reduce photocatalytic activity of the ZnO. One of the efficient ∗ Corresponding author. Tel.: +91 4144 237386; fax: +91 4144 237386. E-mail address: chemshanthi@gmail.com (M. Shanthi). methods to overcome this limitation is the modification of semi- conductors with noble metals [10–16]. The design and modification of ZnO photocatalyst with high sensitivity and reactivity have attracted much attention in recent years. Therefore, the photo- catalytic activity of ZnO should be further enhanced from the viewpoint of practical use. ZnO/Ag composite structure is now an exciting area in research for developing photocatalytic applica- tions. Ag is known as electron sinks due to the Schottky barrier at the metal–semiconductor interface [17,18]. In addition to single semiconductor photocatalyst, many coupled semiconductor sys- tems, such as ZnO–Fe 2 O 3 [19,20], ZnO–WO 3 [19,20], ZnO–SnO 2 [21], TiO 2 –WO 3 [22,23], TiO 2 –SnO 2 [24–28] and TiO 2 –ZnO [29] have been reported for effective environmental remediation. Tung- sten oxide (WO 3 ) is an n-type semiconductor with small band gap of 2.6 eV [30]. Coupling of WO 3 with TiO 2 or ZnO using different preparation methods, such as wet impregnation [31,32], sol–gel [33,34], ball milling [35] and grafting of tungsten alkoxides [36] has been reported. All these preparation procedures influence the dispersibility of WO 3 particles in the TiO 2 or ZnO powder, their coverage on the surface of the semiconductor oxide. A better per- formance using WO 3 in TiO 2 or ZnO system was found under visible light [33,35]. Similarly, under UV light, coupling of WO 3 with TiO 2 had shown better efficiency for the photocatalytic degradation of monocrotophos [35], Acid Red [37], stearic acid and toluene [34,38]. Loading of noble metals on coupled semiconductors was reported to improve the photocatalytic activity [39]. The aim of this study was to assess the photocatalytic activity of WO 3 loaded Ag–ZnO with different content of WO 3 in the degradation of an azo dye AB 1. 1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molcata.2012.09.008