Colloids and Surfaces B: Biointerfaces 67 (2008) 230–237 Contents lists available at ScienceDirect Colloids and Surfaces B: Biointerfaces journal homepage: www.elsevier.com/locate/colsurfb Formation and characterization of surfactant stabilized silver nanoparticles: A kinetic study Shaeel Ahmed AL-Thabaiti, F.M. Al-Nowaiser, A.Y. Obaid, A.O. Al-Youbi, Zaheer Khan ∗ Department of Chemistry, Faculty of Science, King Abdul Aziz University, P.O. Box 80203, Jeddah 21413, Saudi Arabia article info Article history: Received 6 May 2008 Received in revised form 30 August 2008 Accepted 30 August 2008 Available online 6 September 2008 Keywords: Nanoparticles Silver(I) Ascorbic acid CTAB SDS abstract Kinetic data for the silver nitrate–ascorbic acid redox system in presence of three surfactants (cationic, anionic and nonionic) are reported. Conventional spectrophotometric method was used to monitor the formation of surfactant stabilized nanosize silver particles during the reduction of silver nitrate by ascorbic acid. The size of the particles was determined with the help of transmission electron microscope. It was found that formation of stable perfect transparent silver sol and size of the particles depend upon the nature of the head group of the surfactants, i.e., cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and Triton X-100. The silver nanoparticles are spherical and of uniform particle size, and the average particle size is about 10 and 50nm, respectively, for SDS and CTAB. For a certain reaction time, i.e., 30 min, the absorbance of reaction mixture first increased until it reached a maximum, then decreased with [ascorbic acid]. The reaction follows a fractional-order kinetics with respect to [ascorbic acid] in presence of CTAB. On the basis of various observations, the most plausible mechanism is proposed for the formation of silver nanoparticles. © 2008 Published by Elsevier B.V. 1. Introduction The chemistry of nanosize- and colloidal-metal particles in terms of their physicochemical properties in solution has come a long way and their importance in semiconductors, super- conductors, photography, catalyst production, supermagnets, etc. are unlimited [1–10]. Various radiation-, chemical-, photo-, and electro-chemical methods and theories have been used for the preparation and characterization of small particles [11–15]. For stabilization of small particles, the use of polymers, ligands, solid matrix and surfactants has also been suggested [16–20]. Although a number of stabilizers are available for the stabilization of nanosize particles in solution, these are associated with some demerits [21]. In this content, surfactant aggregates, especially micelles, reverse micelles and macroemulsions, will get an edge over other stabiliz- ers [7,19,22–25]. Surfactants role in bulk solution and at interfaces is of great importance in surface chemistry. Surfactants properties have attracted growing attention for use in biological and chemical research applications. Henglein et al. [1] in their pioneering review mentioned that the reactions on the surfaces of small particles are referred to as microelectrode due to the similarities with electrode reactions in electrochemistry. ∗ Corresponding author at: Permanent address: Department of Chemistry, Jamia Millia Islamia (Central University), Jamia Nagar, New Delhi 110025, India. E-mail address: drkhanchem@yahoo.co.in (Z. Khan). Reduction of silver(I) by chemical and radiation chemical meth- ods proceeds through a one-step process to produce a silver sol. Due to these facts, a significant amount of systematic studies have been reported on the formation of still growing microelectrode (GME) silver nanosize metal particles in absence of surfactants [6]. Formation of long-lived clusters of silver by the chemical method (silver(I)-sodium borohydride reaction in presence of polyanion) has been reported by Henglein and his coworkers for the first time [26,27]. On the other hand, it has also been established that ascor- bic acid and hydrazine can also be used for the preparation of silver nanoparticles in presence of surfactants [20,28,29]. The kinetics of ascorbic acid oxidation by transition metal ions are well-documented in literature [30]. The majority of stud- ies have proposed the formation of dehydroascorbic acid as the two-electron transfer oxidation product of ascorbic acid. The com- plexities of ascorbate as a reducing agent have discussed by Creutz [31]. Recently [32], we have reported the oxidation of ascorbic acid by water soluble colloidal MnO 2 . It is believed that redox chemistry of ascorbic acid plays an important role in human nutrition. Thus, the kinetics of the reactions of ascorbic acid in biological systems has become important to bio-, inorganic-, and surface-chemists. The silver particles may be useful, in favorable situations, inves- tigating the kinetics of the oxidative degradation of –N, –O and –S containing toxic organic compounds by silver sol by passing the problems arising from the precipitation of Ag 0 . Recognizing the importance of ascorbic acid in surface chemistry as reducing- and nucleophilic-reagent, we have chosen to study the kinetics 0927-7765/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.colsurfb.2008.08.022