Applied Surface Science 265 (2013) 317–323 Contents lists available at SciVerse ScienceDirect Applied Surface Science j our nal ho me p age: www.elsevier.com/loc ate/apsusc Production of stable hydrosols of crystalline TiO 2 nanoparticles synthesized at relatively low temperatures in diverse media Esin Burunkaya a,b,∗ , Murat Akarsu a,b , H. Erdem C ¸ amurlu c,d,1 , Ömer Kesmez a,b , Zerin Yes ¸ il a,b , Meltem Asiltürk e,2 , Ertu˘ grul Arpac ¸ a,b a Department of Chemistry, Akdeniz University, 07058, Antalya, Turkey b NANOen R&D Ltd., Antalya Technopolis, Akdeniz University Campus, Antalya, Turkey c Department of Mechanical Engineering, Akdeniz University, 07058, Antalya, Turkey d Mattek Advanced Materials Ltd., Antalya Technopolis, Akdeniz University Campus, 07058, Antalya, Turkey e Department of Materials Science and Engineering, Akdeniz University, 07058, Antalya, Turkey a r t i c l e i n f o Article history: Received 18 June 2012 Received in revised form 31 October 2012 Accepted 2 November 2012 Available online 9 November 2012 Keywords: TiO2 Hydrosol Nanoparticle Photocatalysis Reflux synthesis Rhodamine B a b s t r a c t TiO 2 hydrosols were obtained by dispersing nanoparticles synthesized from titanium ethoxide as precur- sor via reflux method without any further thermal treatment. In this study, the reaction parameters such as solvent, type of catalyst, temperature and duration of the synthesis of TiO 2 nanoparticles were exten- sively investigated. The crystalline nanoparticles obtained without calcination have particle size in range of 3.3 nm and 5 nm, and BET surface area of up to 182 m 2 /g. Transparent TiO 2 hydrosols were prepared in both water and non-polar solvent without use of any additional dispersing agent. The synthesized nanoparticles exhibited photocatalytic activity against Rhodamine B dye. © 2012 Elsevier B.V. All rights reserved. 1. Introduction It is a well-known phenomenon that photogenerated radicals of hydroxyl and superoxide upon the illumination of semiconductors such as TiO 2 , ZnO and SnO 2 with a source of ultraviolet or visible light break down organic substances. For this purpose, TiO 2 parti- cles are widely applied because of its low toxicity and cost, and high chemical stability. Besides exhibiting photocatalytic activity, TiO 2 surface becomes superhydrophilic upon illumination, which makes its application possible in wide ranges of areas such as the pro- duction of self-cleaning and anti-fogging surfaces, air purification, photovoltaic devices, and antibacterial surfaces [1–4]. In a recent publication, preparation methods and properties of TiO 2 particles have been comprehensively reviewed by Banerjee [1]. TiO 2 particles can be synthesized through a number of methods ∗ Corresponding author at: Akdeniz Üniversitesi, Fen-Edebiyat Fakültesi, Kimya Bölümü, Dumlupınar Bulvarı, Kampüs, 07058, Antalya, Turkey. Tel.: +90 242 310 2327; fax: +90 242 227 8911. E-mail address: esinburunkaya@gmail.com (E. Burunkaya). 1 Akdeniz Üniversitesi, Makine Mühendisli˘ gi Bölümü, Dumlupınar Bulvarı, Kam- püs, 07058, Antalya, Turkey. 2 Akdeniz Üniversitesi, Malzeme Bilimi ve Mühendisli˘ gi Bölümü, Dumlupınar Bul- varı, Kampüs, 07058, Antalya, Turkey. including sol–gel [5,6], from inorganic salts as precursor [7], ultra- sonic technique [8], reflux synthesis [9] and hydrothermal method [6,10–12]. In most of these studies, the synthesized particles have been calcined to obtain crystalline TiO 2 , which increases the par- ticle size leading to a reduction in the total surface area and the photocatalytic efficiency [11]. Among these methods, hydrothermal and reflux synthesis methods result in crystalline TiO 2 particles, therefore the calci- nation step can be eliminated. It is crucial to obtain crystalline TiO 2 nanoparticles well dispersed in terms of obtaining transpar- ent and photocatalytically active films on substrates, particularly heat-sensitive ones such as plastics, wood and fibers to preserve the genuine appearance of the applied substrate. The translucent sols of monodisperse TiO 2 nanoparticles, so-called hydrosols, have been synthesized by hydrothermal treatment, where crystalliza- tion of hydrated TiO 2 into anatase or rutile phase occurs in water or organic solvents at temperatures higher than their boiling point under high pressure [13,14]. Disadvantages of this method include the need of expensive autoclaves and high safety requirements for industrial uses. In the reflux method, reaction takes place in a container, which is heated at relatively low temperatures depending on the boiling point of the solvent. The container is connected to a cooled reflux condenser system open to atmosphere. The vaporized solvents are 0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2012.11.003