Journal of Molecular Catalysis A: Chemical 396 (2015) 290–296 Contents lists available at ScienceDirect Journal of Molecular Catalysis A: Chemical jou rnal h om epa ge: www.elsevier.com/locate/molcata Facile synthesis of heterostructured Ag-deposited SiO 2 @TiO 2 composite spheres with enhanced catalytic activity towards the photodegradation of AB 1 dye K.P.O. Mahesh, Dong-Hau Kuo ∗ , Bo-Rong Huang Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan a r t i c l e i n f o Article history: Received 21 April 2014 Received in revised form 15 October 2014 Accepted 15 October 2014 Available online 24 October 2014 Keywords: SiO2@TiO2 composite spheres Ag nanoparticles Photocatalysts Dye degradation a b s t r a c t Ternary Ag–SiO 2 @TiO 2 heterostructured composite spheres were synthesized and investigated as a cata- lyst for the photodegradation of Acid Black 1 (AB 1) in an aqueous solution. The SiO 2 spheres (310 nm) and SiO 2 @TiO 2 composite spheres (320 nm) were prepared without aggregation by the sol–gel method using tetraethyl orthosilicate (TEOS) and Ti(iBuO) 4 as precursors. Different concentrations of Ag nanoparticles were photodeposited on SiO 2 @TiO 2 spheres with particle sizes of about 10 nm. The Ag nanoparticles on the SiO 2 @TiO 2 composite spheres (Ag–SiO 2 @TiO 2 ) were extensively characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning microscopy (FE-SEM), transmis- sion electron microscopy (TEM), UV-diffuse reflectance spectroscopy, and electrochemical impedance spectroscopy (EIS). The photocatalytic activity of the Ag–SiO 2 @TiO 2 photocatalyst towards AB 1 under UV irradiation was studied. The effects of the operational parameters such as the different Ag contents on the SiO 2 @TiO 2 composite spheres, as well as the effect of the initial concentration of the dye solution on photomineralization were analyzed. The results showed the Ag–SiO 2 @TiO 2 photocatalyst to be efficient and reusable. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Nowadays, organic dyes are one of the foremost groups of pol- lutants found in wastewater produced by various industries. It is estimated that roughly 700,000 tons of dyes are produced per annum around the world. Of this amount about 20% is unloaded as industrial waste without prior action or treatment [1]. The effi- cient removal of organic dye stuffs from industrially polluted water remains an important and challenging issue in the field of environ- mental remediation and pollution control. Semiconductor-based heterogeneous photocatalysts have been widely used to remove the dye stuffs in aqueous solutions [2–5]. Titanium dioxide is one of the most important semiconductor photocatalysts due to its high chemical stability, low cost, easy availability, and non-toxic nature, all of which have combined and led to intense research attention and a broad range of applications such as for photocatalysts [6–9], sensors [10,11], solar cells [12,13], and lasers [14]. However, the large band gap and high recombina- tion rate of the photogenerated electron–hole pairs tend to reduce ∗ Corresponding author. Tel.: +886 2 27303291; fax: +886 2 27303291. E-mail address: dhkuo@mail.ntust.edu.tw (D.-H. Kuo). the complete utilization of UV and solar energy. Also, it is very diffi- cult to recover the TiO 2 nanoparticles from a dye solution. In order to overcome these problems, the larger SiO 2 particles have been used as a carrier/support for the dispersion of TiO 2 nanoparticles on a surface. They can increase the active surface area of the TiO 2 catalyst so as to facilitate the recycling process. Several studies have used the SiO 2 @TiO 2 nanocomposite as a photocatalyst and reported a very good photocatalytic activity compared to the TiO 2 catalyst. The nano-sized SiO 2 can not only be used as a substrate to absorb organic pollutants and to make contact with the active sites on TiO 2 particles, but also helps to disperse the very small sized TiO 2 particles on the SiO 2 surface [15–17]. To further limit the recombination of electron–hole pairs, inert metallic nanostructures such as Ag, Au, Pt or Pd have been deposited on the TiO 2 nanoparticles in order to increase the life time of the electron–hole pairs [18–20]. Among these metal catalysts, Ag is one of the cheapest, most stable, and easily available, and also has the advantage that it can be easily deposited on the surface of SiO 2 @TiO 2 spheres. Zhao et al. and Xu et al. reported on the embed- ding of Ag nanoparticles on a SiO 2 /TiO 2 film and confirmed that the Ag nanoparticles helped to enhance the photocatalytic activ- ity of the SiO 2 /TiO 2 film [21,22]. Chen et al. prepared SiO 2 /TiO 2 nanocomposites by the solvothermal method and deposited Ag http://dx.doi.org/10.1016/j.molcata.2014.10.017 1381-1169/© 2014 Elsevier B.V. All rights reserved.