Applied Catalysis B: Environmental 106 (2011) 212–219 Contents lists available at ScienceDirect Applied Catalysis B: Environmental journa l h o me pa ge: www.elsevier.com/locate/apcatb Gram-scale wet chemical synthesis of wurtzite-8H nanoporous ZnS spheres with high photocatalytic activity Yong Liu a , Juncheng Hu a , Chilan Ngo b , Sergey Prikhodko b , Suneel Kodambaka b , Jinlin Li a , Ryan Richards c,∗ a Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, South-Central University for Nationalities, Wuhan 430074, PR China b Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, CA 90095, USA c Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401, USA a r t i c l e i n f o Article history: Received 23 March 2011 Received in revised form 2 May 2011 Accepted 18 May 2011 Available online 27 May 2011 Keywords: Nanoporous ZnS spheres Wurtzite Photocatalysis Organic pollutants Hydroxyl radical ( • OH) Photoluminescence technique a b s t r a c t Wurtzite-8H nanoporous ZnS spheres assembled from crystallites, were synthesized via a “green” wet chemical route. A possible formation mechanism for the growth process of the ZnS spheres has been proposed based on experimental observations. The prepared catalysts are characterized by transmission electron microscopy, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, N 2 adsorption–desorption isotherms, elemental analysis, and UV–vis absorption spectroscopy. The catalyst showed high and stable photocatalytic activ- ity for the degradation of persistent toxic organic pollutants, as demonstrated with azo dye X-3B (X-3B), trichloroacetate (TCA) and phenol under both visible (>420 nm) and UV light irradiation. The experimen- tal results demonstrate that the photocatalytic activity of ZnS spheres is 3.3 and 9 times higher than that of Degussa P25 and commercial ZnS, respectively. The production of • OH radicals on the ZnS surface was detected by the photoluminescence (PL) technique using coumarin as a probe molecule, which suggests that • OH radicals are the dominant photo-oxidant in the photocatalytic reaction. More importantly, this synthesis method can be economical for a scale-up process, and may also be applicable to the preparation of additional II–VI semiconductors for catalysis and other applications. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Photocatalysis by semiconductor oxides is a conventional tech- nology that has been widely applied to degrade organic and inorganic pollutants both in vapour and liquid phase [1–8]. TiO 2 is currently the best known and most widely used photocatalyst due to its low cost and stability [9–12]. However, there are still two main challenges to be overcome. First, the low quantum efficiency and high band gap of semiconductor oxides limit their photocatalytic activity under visible light. Thus, developing a straightforward and general method for one-step synthesis of highly efficient and stable catalysts working with solar energy as a free “green” light source is an attractive and challenging issue for material scientists. Second, most studies report on syntheses of photocatalysts of only micro- to milli-molar amounts with intrinsically high cost. Therefore, the development of cost-effective methods suitable for the large-scale ∗ Corresponding author. Tel.: +1 303 273 3612; fax: +1 303 273 3629. E-mail addresses: junchenghuhu@hotmail.com (J. Hu), Kodambaka@ucla.edu (S. Kodambaka), rrichard@mines.edu (R. Richards). synthesis of photocatalysts is of great importance and a challenge for their industrial applications. Recently, transition-metal sulfides, in particular ZnS have attracted much attention because of their unique properties and potential applications. ZnS nanocrystals possess two crystal struc- tures, cubic sphalerite and hexagonal wurtzite with different properties. The wurtzite ZnS, which is stable at temperatures higher than 1020 ◦ C [13,14], is much more interesting and desirable for its optical properties than the sphalerite phase [15]. Hu et al. [16] recently reported a precursor thermolysis route to produce ZnS nanoporous particles composed of wurtzite ZnS nanocrystals. In their study, ZnS particles showed high photodegradation efficiency of eosin B only in the UV region, and to present, visible light-active ZnS was only obtained by doping with metal ions such as Ni [17], Cu [18], Pb [19,20], or non-metallic elements such as C or N [21]. Herein, we report, for the first time, a template-free “green” wet chemical route for the gram-scale synthesis of nanoporous spheres (about 600 nm in diameter) composed of hexagonal wurtzite ZnS crystallites on the basis of our previous work [22–25]. This wet chemical route has the following advantages: (i) for the cata- lyst, it can work efficiently under both visible and UV irradiation; (ii) the route is inexpensive and suitable for the gram-scale 0926-3373/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2011.05.028