Contents lists available at ScienceDirect Materials Science in Semiconductor Processing journal homepage: www.elsevier.com/locate/mssp Synthesis of CdS quantum dots in an imidazolium based ionic liquid Zikhona Tshemese a , Sixberth Mlowe a, ⁎ , Neerish Revaprasadu a , Nirmala Deenadayalu b a Chemistry Department, University of Zululand, Private Bag X1001, Kwadlangezwa 3886, South Africa b Department of Chemistry, Durban University of Technology, P.O. Box 1334, Durban 4000, South Africa ARTICLE INFO Keywords: CdS Ionic liquid Thermolysis Optical properties ABSTRACT A solution protocol to synthesize CdS quantum dots (QDs) using 1-ethyl-3-methylimidazolium methanesulfonate ionic liquid is described in this work. Various reaction parameters such as temperature and injection protocols were varied to study the optical and structural properties of the obtained particles. X-ray diffraction (XRD) studies confirmed the formation of cubic and hexagonal phases depending on the reaction conditions. Peak broadening in the diffraction patterns revealed the formation of small sized quantum dots and the morphological studies further showed formation of nano-sized particles in the range of 2–15 nm, with close to spherical shaped morphologies. Blue-shifted band gaps further confirmed formation of very small CdS nanoparticles, which de- pendent on the reaction temperatures. 1. Introduction Cadmium sulfide (CdS) is a group II-VI semiconductor with a band gap of 2.42 eV [1–3], with interesting optical and electrical properties suitable for various technological applications [4,5]. These novel properties are harnessed in light emitting diodes [6], thin film tran- sistors [7], photocatalysis [8,9], photovoltaic cells [10] and non-linear optical devices [11]. Different synthetic approaches have been em- ployed to obtain CdS nanoparticles. High quality, monodispersed na- noparticles for example have been fabricated by high temperature so- lution based methods, usually using high boiling organic solvents such as tri-n-octylphosphine oxide (TOPO) and alkylamines [12–19]. In general these conventional solvents are harsh, nasty, air sensitive and inherently toxic, posing hindrance for applications especially in biolo- gical systems. The current focus is on the use of environmentally benign solvents as a tool to shape a more sustainable future. The ionothermal synthetic method, which makes use of ionic liquids (ILs) as solvents has been identified as a suitable greener route to nanoparticle synthesis [20–23]. There are reports on metallic nanoparticles, metal oxides and other semiconductor nanomaterials being made using ionic liquids [24–32]. Biswas et al. have fabricated hexagonal CdS nanoparticles with a dia- meter of 3–13 nm using imidazolium based ionic liquids [29]. Different nanoparticle sizes were obtained by changing the anions of the ionic liquid. Green and co-workers prepared monodispersed spherical CdSe nanoparticles using the phosphonium based ionic liquid (trihexyl(tet- radecyl))phosphonium bis(2,4,4-trimethylpentylphosphinate) as a sol- vent and capping agent [30]. Short nanorods, quasi nanospheres and faceted CdS nanoparticles were successfully synthesized with sizes ranging from about 4.2–44 nm via thermal decomposition of cadmium complexes with trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethyl pentylphosphinate) [31]. Recently 1-hexyl-3-methylimidazolium tet- rafluroborate with cadmium diethyldithiocarbamate and hex- adecylamine have been used to prepare CdS nanoparticles with a spherical shape and diameter of 5 nm [32]. We report the use of 1-ethyl-3-methylimidazolium methanesulfo- nate ionic liquid (ESI Fig. S1) as a replacement for the conventional solvents to synthesize CdS nanoparticles. This solvent is liquid at room temperature with cationic and anionic species. To the best of our knowledge, this ionic liquid has never been reported for the synthesis of CdS nanoparticles. The CdS quantum dots reported here showed monodispersity, small sizes and good size-dependent optical properties. 2. Experimental 2.1. Materials All chemicals used were of high purity (analytical grade). Cadmium acetate dihydrate, 1-dodecanethiol and 1-ethyl-3-methylimidazolium methanesulfonate were purchased from Sigma-Aldrich. Acetone and ethanol were supplied by Prestige laboratory and were used as received. 2.2. General procedures for the synthesis of CdS nanoparticles using 1- ethyl-3-methylimidazolium methanesulfonate Three approaches were employed to synthesize CdS nanoparticles http://dx.doi.org/10.1016/j.mssp.2017.08.009 Received 22 March 2017; Received in revised form 15 June 2017; Accepted 6 August 2017 ⁎ Corresponding author. E-mail address: sixb2809@gmail.com (S. Mlowe). Materials Science in Semiconductor Processing 71 (2017) 258–262 1369-8001/ © 2017 Elsevier Ltd. All rights reserved. MARK