Journal of Hazardous Materials 250–251 (2013) 370–378 Contents lists available at SciVerse ScienceDirect Journal of Hazardous Materials jou rnal h om epa ge: www.elsevier.com/locate/jhazmat High-performance pure and Fe 3+ -ion doped ZnS quantum dots as green nanophotocatalysts for the removal of malachite green under UV-light irradiation Hamid Reza Rajabi a,∗ , Omid Khani b , Mojtaba Shamsipur c , Vahid Vatanpour d a Chemistry Department, Yasouj University, Yasouj 75918-74831, Iran b Electroceramics Research Center, Malek-Ashtar University of Technology, Shahin Shahr, Iran c Department of Chemistry, Razi University, Kermanshah, Iran d Faculty of Chemistry, Kharazmi (Tarbiat Moallem) University, Tehran, Iran h i g h l i g h t s ◮ Synthesis of ultra-small ZnS and ZnS:Fe QDs in aqueous media. ◮ Characterization of QDs by TEM, XRD, FAAS and UV–vis absorption tech- niques. ◮ The new report on the photocatalytic behavior of QDs on removal of MG. ◮ Effective degrade of dye by novel modified QDs up to 98%. g r a p h i c a l a b s t r a c t 0 1 2 3 4 190 230 270 310 350 390 430 Wavelength (nm) Absorbance (A.U.) a r t i c l e i n f o Article history: Received 15 September 2012 Received in revised form 5 February 2013 Accepted 9 February 2013 Available online xxx Keywords: ZnS Zn1-xFexS Quantum dots Nanophotocatalysts Photodecolorization Malachite green a b s t r a c t The heterogeneous photocatalysis using UV-radiation and quantum dots (QDs) is an interesting method for the treatment of water polluted with the organic substances. In this study, ZnS QDs, as a pure and doped with Fe 3+ , were prepared for photodecolorization of malachite green (MG) as a model dye. The synthesis of QDs was carried out using a chemical precipitation method in aqueous solution, in the presence of 2-mercaptoethanol as a capping agent. The XRD patterns indicated that the doped nanoparticles are crystalline, with cubic zinc blend structure. The effects of dopant content, pH, nanophotocatalyst amount, irradiation time, and initial dye concentration on the removal efficiency of MG were studied. Results showed that the QDs presented high MG decolorization efficiency, and doping with Fe 3+ promoted the dye removal. The maximum removal of dyes was obtained at 80 mg/L of photocatalyst as an optimum value for the dosage of photocatalyst in pH of 8.0. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Quantum dots (QDs) are zero-dimensional semiconductors that may be used in a wide array of fields. QDs are nanometer-scale semiconductor crystals composed of groups II–VI or III–V elements, and are defined as particles with physical dimensions smaller than the exciton Bohr radius [1], which is the characteristic distance ∗ Corresponding author. Tel.: +98 741 2242164; fax: +98 741 2242164. E-mail address: h.rajabi@mail.yu.ac.ir (H.R. Rajabi). between an excited electron and its hole within a given material. This confines the electron–hole pair and causes the particles to possess specific material properties, such as shifted emission spec- tra, which are distinctly different from bulk properties of the same semiconductor material. A typical QD has a diameter ranging from 2 to 20 nm with size comparable to a large protein. When a photon of light hits such a semiconductor, some of their electrons are excited into higher energy states. When they return to their ground state, a photon of a frequency characteristic of that material is emitted [2]. Among the wide-bandgap semiconductors, zinc sulfide (ZnS) has a large exciton binding energy (40 eV) and a small Bohr radius 0304-3894/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2013.02.007