Applied Catalysis B: Environmental 144 (2014) 29–35 Contents lists available at SciVerse ScienceDirect Applied Catalysis B: Environmental jo ur nal ho me p age: www.elsevier.com/locate/apcatb Preparation of Cu-doped ZnS QDs/TiO 2 nanocomposites with high photocatalytic activity Houcine Labiadh a , Tahar Ben Chaabane a , Lavinia Balan b , Nidhal Becheik c , Serge Corbel c , Ghouti Medjahdi d , Raphaël Schneider c,∗ a Unité de Recherche UR11ES30 de Synthèse et Structures de Nanomatériaux, Université de Carthage, Faculté des Sciences de Bizerte, 7021 Jarzouna, Tunisia b Institut de Science des Matériaux de Mulhouse (IS2M), LRC 7228, 15 rue Jean Starcky, 68093 Mulhouse, France c Université de Lorraine, Laboratoire Réactions et Génie des Procédés (LRGP), UMR 7274, CNRS, 1 rue Grandville, BP 20451, 54001 Nancy Cedex, France d Université de Lorraine, Institut Jean Lamour (IJL), UMR 7198, CNRS, BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex, France a r t i c l e i n f o Article history: Received 14 March 2013 Received in revised form 27 June 2013 Accepted 2 July 2013 Available online xxx Keywords: Cu-doped zinc sulfide Titanium dioxide Oxidation Photocatalysis a b s t r a c t Cu-doped ZnS quantum dots (QDs) were synthesized in aqueous solution using 3-mercaptopropionic acid (MPA) as stabilizer. Transmission electron microscopy (TEM) results indicate that the Cu:ZnS nanocrys- tals distribute uniformly and the size is ca. 2.9 ± 0.5 nm. These nanocrystals were successfully associated to anatase TiO 2 nanoparticles to yield TiO 2 /Cu:ZnS photocatalysts. Morphological and optical proper- ties of TiO 2 /Cu:ZnS nanocomposites were characterized by X-ray diffraction (XRD) analysis, TEM, and UV–vis and fluorescence spectroscopies. Photocatalytic activities of TiO 2 /Cu:ZnS nanocomposites were evaluated by the oxidation of salicylic acid aqueous solutions under UV light irradiation. Enhanced per- formances compared either to pure TiO 2 nanoparticles or to undoped TiO 2 /ZnS nanocomposites were observed. Effects of the mass ratio of the TiO 2 and Cu:ZnS and of the pH of the aqueous solution contain- ing salicylic acid on the photocatalytic activities of TiO 2 nanoparticles sensitized with Cu:ZnS QDs were also investigated. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Over the last years, photocatalytic degradation has received much attention as an alternative method in the removal of envi- ronmental pollutants in aqueous phase as well as in gaseous media. Titanium dioxide (TiO 2 ) was recently confirmed as one of the most potential semiconductor for degradation of unwanted and toxic organic compounds, removal of pollutants in contaminated water and air, and killing of harmful bacteria [1–5]. During photocatalysis experiments with TiO 2 , electrons (e - ) and holes (h + ) are gener- ated at the surface of TiO 2 and are converted into excitons in quantum states near the surface after energy relaxation. During this process, a fast e - –h + recombination takes place to form the luminescent exciton states, and thus the charge carriers are not so efficiently transferred to substrate for redox reaction. Among the four polymorphs of TiO 2 found in nature, the anatase phase is the most photoactive because photogenerated charge carriers recom- bine at the lowest rate in anatase and many organic molecules readily interact with the anatase surfaces [6–8]. To increase the photocatalytic reaction rates, the photogenerated e - and h + must be separated into different locations on the catalyst. This can be ∗ Corresponding author. Tel.: +33 3 83 17 50 53. E-mail address: raphael.schneider@univ-lorraine.fr (R. Schneider). achieved by deposition of another semiconductor, generally quan- tum dots (QDs), at the surface of TiO 2 to form a heterojunction structure and thus enhance the catalytic performance of photo- catalysts [9,10]. Once both semiconductors excited by light, e - accumulate at the low-lying conduction band of one semiconduc- tor while h + accumulate at the valence band of the other material. These processes of charge separation are very fast and the efficiency of reduction or oxidation of the adsorbed organics remarkably increases. TiO 2 /CdS [11–14], TiO 2 /CdSe [15–17], TiO 2 /PbS [18–20] or TiO 2 /PbSe [21,22] heterojunctions have been widely studied in recent years to decompose contaminants effectively. This inter- est is due to the fact that QDs are photostable and that their optic and electronic properties can be adjusted by changing their size and shape. Moreover, CdS, CdSe, PbS or PbSe QDs possess ener- getically high-lying conduction bands, and can thus prevent e - –h + recombination due to efficient spatial separation of photogenerated charge. However, in view of recent environmental regulations, the high toxicity of cadmium or lead introduces a doubt on the future applicability of this kind of QDs. Thus, several heavy metal-free alternative materials like CuInS 2 [23] or AgGa 1-x In x S 2 [24] have been proposed to replace Cd- or Pb-based QDs. Although being a wide band gap semiconductor, ZnS nanocrys- tals can also be associated to TiO 2 to increase its photocatalytic activity because of their high potentials of conduction band e - and 0926-3373/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcatb.2013.07.004