Surfactant effects on the particle size of iron (III) oxides formed by sol–gel synthesis Erin Camponeschi a , Jeremy Walker a , Hamid Garmestani a , Rina Tannenbaum a,b, * a School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA b Department of Chemical Engineering, Technion – Israel Institute of Technology, Haifa, Israel article info Article history: Received 28 June 2007 Received in revised form 10 April 2008 Available online 30 July 2008 Keywords: Nanoparticles, colloids and quantum structures Polymers and organics Sol–gel, aerogel and solution chemistry abstract In this work, we probed the effects of a common surfactant, sodium dodecylbenzene sulfonate (NaDDBS), on the particle size of iron (III) oxides formed via a modified sol–gel synthesis. The goal was to create tun- able nanosized particles via a method that combines the efficiency and advantages of the sol–gel process, but inhibits the formation of a gel. Two different metal salt precursors were used, ferric nitrate nonahy- drate, Fe(NO 3 ) 3  9H 2 O, and ferric chlorate hexahydrate, FeCl 3  6H 2 O. The particle size of the dried gel was 4.5 nm for Fe(NO 3 ) 3  9H 2 O and 3.6 nm for FeCl 3  6H 2 O. In the presence of the surfactant FeCl 3  6H 2 O formed a gel and Fe(NO 3 ) 3  9H 2 O was unable to gel, but the new particle sizes were 4.9 nm and 3.2 nm, respectively. The addition of the surfactant in the later stages of the process afforded the stabil- ization of independent nanoparticles of the same size as those obtained in the systems that gelled. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction The design, development, manufacturing and utilization of nanomaterials have become very broad and vigorously growing fields of research in recent years [1–17]. Nanomaterials represent a new class of materials that possess distinctive physical and chemical properties that differ substantially from their micron-size and bulk counterparts [3–5,7,8,10,12–19]. In order to harvest and translate the fascinating properties of materials at the nanoscale size domain into viable, affordable new technologies, it is impera- tive that new, facile synthesis and manufacturing methods could be developed in order to create the fundamental building blocks of the nanomaterials and their subsequent assembly into useful devices. These new methods should afford a high degree of repro- ducibility in terms of nanomaterial size, structure and morphology and also allow process scale-up without adverse effects on the quality of the products [17,20–22]. Of the multitude materials of interest, iron oxide nanoparticles offer a potential compatibility as material building blocks for a par- ticularly broad range of applications, such as magnetic materials, catalysts, sensors (chemical, electronic and biological), data storage materials, MRI contrast agents and drug delivery facilitators [7,8,10,12–15,17,19,21]. Hence, the design, synthesis and large scale manufacturing of various types iron oxides with tight control on particle size, size distribution and particle geometry and mor- phology, has become one the most important research avenues in the area of nanomaterials synthesis. There are currently several different methods for creating iron oxide nanoparticles such as sol–gel processing, synthesis using microemulsions, hydrothermal synthesis, and high temperature reactions in solution [7,8,10,12–15,17,21]. All the above-men- tioned methods, with the exception of the sol–gel synthesis, con- stitute reliable and controllable methods for the formation of iron oxide nanoparticles, however, they require high temperature, high pressure and/or hazardous environments, which can be diffi- cult and costly to produce in bulk [7,17,23,24]. Conversely, sol–gel synthesis does provide an extremely easy method of creating a large variety of metal oxides from metals salts, at low tempera- tures and ambient conditions. The reaction proceeds via the fol- lowing pathway: M III ðAnion 1 Þ 3  xH 2 O ! EtOH Gelation agent M III 2 O 3 ð1Þ The process involves the scavenging of protons from the aqueous coordination sphere of the metal salt (sol formation), followed by condensation and formation of the metal oxide product character- ized by a three-dimensional network [7,17]. The process is facili- tated by the addition of a gelation agent, such as propylene oxide. This molecule acts as an effective proton scavenger from the water molecules in the immediate coordination sphere of the hydrated metal complex, resulting in a protonated epoxide. The protonated epoxide subsequently undergoes irreversible ring-opening by react- ing with a nucleophile present in solution, either a nitrate ion, a chloride ion or water. Then, as a result of this ring-opening reaction in which a protonated diol is formed, deprotonation occurs and a diol is formed in conjunction with a net elimination of protons from 0022-3093/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2008.04.018 * Corresponding author. Address: School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA. Tel.: +1 404 385 1235; fax: +1 404 894 9140. E-mail address: rina.tannenbaum@mse.gatech.edu (R. Tannenbaum). Journal of Non-Crystalline Solids 354 (2008) 4063–4069 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol