Colloids and Surfaces A: Physicochem. Eng. Aspects 338 (2009) 20–24 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa Synthesis of CdS nanocrystals stabilized with sodium citrate Thelma Serrano a , Idalia Gómez a,∗ , Rafael Colás b , José Cavazos b a Centro de Laboratorios Especializados, Facultad de Ciencias Químicas, Universidad Autónoma de Nuevo León, Mexico b Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, Mexico article info Article history: Received 4 October 2007 Received in revised form 28 November 2008 Accepted 11 December 2008 Available online 24 December 2008 Keywords: Synthesis Microwave radiation Stabilization Nanoparticles abstract The results on the study of the synthesis of cadmium sulfide nanoparticles in sodium citrate solutions using microwave radiation are presented. CdCl 2 and thioacetamide solutions were prepared with three different concentrations of sodium citrate, 2.0, 1.5 and 1.0mM respectively, keeping constant a pH of 8, heating was carried out in a microwave oven for 60 s. Synthesis of nanoparticles were confirmed by differ- ent experimental techniques. The material was arranged as light sensitive cubic particles of nanometric size. Ultraviolet spectroscopy shows that the energy of the band gap is affected by the size of the particles. It was found that the size and aspect of the particles changed as a function of time when held at 86 ◦ C. © 2009 Published by Elsevier B.V. 1. Introduction Work in nanotechnology allows for new materials as well as for the modification of already existing ones to achieve characteristics and properties not observed in average-size crystals [1,2]. Synthe- sis and characterization of semiconductors are of interest to this field because their quantum states depend on the size and self- organization of nanocrystals [3–6]. Cadmium sulfide exhibits interesting chemical, physical and optoelectronic properties and has a high potential use in micro- electronic, catalytic and bioanalytical applications, owing to its nonlinear optical and luminescence properties [1–3,7]. CdS nanoparticles have been obtained by different methods such as syn- thesis in anionic polymers, membranes, micelles, porous glasses, zeolites and physical evaporation [8–13]. All these methods are conducted at relativity high temperatures or use toxic agents such as H 2 S or organometallic precursors. In 2006, Martínez et al. [14] developed a method to synthesize CdS nanoparticles using sim- ple precursors such as CdCl 2 and thioacetamide (CH 3 CSNH 2 ) and microwave heating. The interest in possible uses of CdS in micro- electronic systems is the driving force for developing synthesizing methods capable to obtain stable colloidal nanosize particles. Advances on the control of crystal sizes is required to obtain well defined characteristics and morphologies, some of the mech- ∗ Corresponding author at: Lab. de Vía Húmeda y Sol–Gel, Facultad de Ciencias Químicas, Av. Pedro de Alba s/n, Cd. Universitaria, San Nicolás de los Garza, N.L., C.P. 66400, Mexico. Tel.: +52 81 83294010x6362; fax: +52 81 83765375. E-mail address: mgomez@fcq.uanl.mx (I. Gómez). anisms used to control nanocrystal sizes rely on forcing defined space arrangements [15–18], artificial assembling [15] or preferen- tial nuclei growth [15,19,20]. The methods for stabilization interact with electrostatic forces; chemicals substances used for this pur- pose affect the coordination reactions and promote growth in different directions by stabilizing free electronic pairs present in the molecular structure [19,20]. The surface modification of the particles can be made by the use of ligands that can introduce a high level of self-organization. Some studies on the surface modification of II–VI semiconductors with different organic ligands such as dyes, aromatic hydrocarbons have been performed. [21] Sodium citrate is one of the most com- mon agents used in the synthesis of metallic and semiconductor nanoparticles because it can act as a reducing agent or as a coordi- nation agent. This is due to free electron pairs in the carbonyl group, which stabilize semiconductor nanoparticles by electrostatic forces generated in the system, and it can also act as coordination agent in compounds with metallic atoms with free orbitals [20,21]. The aim of the present work is to present the results of a study on the influence of sodium citrate concentration, which acts as sta- bilizer, on the morphology adopted by CdS nanoparticles processed by microwave heating. 2. Experimental procedure The raw materials used in this work such as thioacetamide (CH 3 CSNH 2 ), CdCl 2 , KOH and sodium citrate were obtained with purities above 99.0%, therefore no further purification was required; all solutions were prepared using Milli-Q water as solvent. 0927-7757/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.colsurfa.2008.12.017