Growth, stability, optical and photoluminescent properties of aqueous colloidal ZnS nanoparticles in relation to surfactant molecular structure S.K. Mehta a,⇑ , Sanjay Kumar b , Michael Gradzielski c a Department of Chemistry and Centre for Advanced Studies in Chemistry, Panjab University, Chandigarh 160 014, India b Department of Chemistry, Govt. College, Chowari (Chamba), HP, India c TU Berlin, Institut für Chemie, Stranski-Laboratorium für Physikalische Chemie und Theoretische Chemie, Sekr. TC 7, Strasse des 17, Juni 124, D-10623 Berlin, Germany article info Article history: Received 25 February 2011 Accepted 19 April 2011 Available online 28 April 2011 Keywords: ZnS Surfactants Adsorption Ostwald ripening Photoluminescence Zeta potential abstract The interaction between organic molecules and the surface of nanoparticles (NPs) strongly affects the size, properties and applications of surface-modified metal sulfide semiconductor nanocrystals. From this viewpoint, we compared the influence of cationic surfactants with various chain lengths and anionic sur- factants with different head groups, as surface modifiers during synthesis of ZnS NPs in aqueous medium. The surfactant adsorbs on the surface of the particles as micelle-like aggregates. These aggregates can form even at the concentration lower than critical micelle concentration (cmc) due to interaction between the polar groups and the NPs. The nature of interaction depends specifically on the surfactant polar group. The ability of surfactant to form the micelle-like aggregates on the surface of the NPs corre- lates with their cmc. This leads to the fact that the surfactant with longer tail stabilizes the NPs better since its cmc is lower. The adsorption of the surfactant on the NPs also stabilizes them by the change of their charge which is in accordance with the correlation of zeta potential with the particles stability. The energetics of surface states generating interesting photoluminescence (PL) properties in ZnS NPs has been governed by the nature of surfactant molecules. In general, the size, structure, and stability of the ZnS NPs can be controlled by the choice of suitable surfactant. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction Facile approaches to assemble the components of the next gen- eration technologies such as the semiconductor nanocrystals (NCs) with controlled morphology and surface electronic states represent a significant challenge in the field of nanoscaled sciences. The interest in these nanomaterials is motivated by the unique optical, electrical and photoluminescent properties induced by the quan- tum size effect which made them promising materials for various potential applications including electronics, optics, and biosensors [1–6]. To date, various strategies have been developed for NPs syn- thesis in aqueous media; however, arrested precipitation via sur- factant-assisted pathways has been evolved as most simple and beneficial in the view of environmental concerns. Additionally, the organic surrounding environment and surface passivation can provide stability and additional functionality to the NPs [7]. Among numerous recent studies [8–13] which mainly focused on surface- modified metallic and semiconductor NPs with a variety of surfac- tants, only few provide suitable discussions on how the surfactant molecules bound onto the surface and affect the growth as well as surface related properties of NPs in aqueous colloidal form. Dhanam et al. [14] have successfully selected concentrations of nonionic surfactant, Triton X-100 (t-octyl-(OCH 2 CH 2 ) x OH, x = 9, 10) to produce one dimensional ZnS nanomaterials instead of three dimensional NPs. Khiew et al. [15] explained the self-assembling of the chitosan laurate surfactant in water as unique architecture to be adopted as the reaction template for the formation of ZnS nanomaterials in 2–10 nm range exhibiting strong quantum con- finement. A generalized, single-step synthesis procedure to coat individual cetyltrimethyl ammonium bromide- (CTAB) capped Au nanorods and CTAB-transferred CdSe/ZnS quantum dots with a thin layer of mesoporous silica has been outlined by Gorelikov and Matsuura [16]. As demonstrated in these studies, it can be generalized that the added stabilizers (surfactants) have some preferred chemical moi- ety which bind to the NPs surface, hinder their unlimited growth and eventually yield a preferred size of the particles defined by the arrangement of surfactant molecules around the inorganic nanosized core. The repulsive force between particles that prevent their agglomeration can be due to electrostatic repulsion or steric exclusion. However, the different surfactant systems reported in individual studies in entirely different environments make it very 0021-9797/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2011.04.079 ⇑ Corresponding author. Fax: +91 172 2545074. E-mail address: skmehta@pu.ac.in (S.K. Mehta). Journal of Colloid and Interface Science 360 (2011) 497–507 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis