Colloids and Surfaces A: Physicochem. Eng. Aspects 265 (2005) 23–31 Preparation and photoactivity of nanostructured TiO 2 particles obtained by hydrolysis of TiCl 4 Maurizio Addamo, Vincenzo Augugliaro, Agatino Di Paola ∗ , Elisa Garc´ ıa-L´ opez, Vittorio Loddo, Giuseppe Marc` ı, Leonardo Palmisano Dipartimento di Ingegneria Chimica dei Processi e dei Materiali, Universit` a di Palermo, Viale delle Scienze, 90128 Palermo, Italy Received 22 July 2004; received in revised form 26 October 2004; accepted 11 November 2004 Abstract This work reports the preparation of nanostructured polycrystalline TiO 2 photocatalysts obtained by hydrolysis of TiCl 4 in very mild conditions. Several samples were prepared as suspensions or colloidal dispersions by using TiCl 4 /H 2 O volume ratios ranging between 1:1 and 1:100. The samples were characterised by X-ray diffraction analysis, specific surface area determination, diffuse reflectance spectroscopy and scanning electron microscopy. 4-Nitrophenol photodegradation was used as probe reaction to test the photoactivity of the catalysts. Some samples revealed a photoactivity higher than that of Degussa P25 in similar experimental conditions and the most photoactive one was that prepared by using the TiCl 4 /H 2 O volume ratio equal to 1:50. A dialysis process was performed in some cases to reduce the amount of chloride ions present in the system. The presence of Cl - ions appeared to be dramatically detrimental for Degussa P25 while a lower influence was found for the home prepared samples. © 2005 Elsevier B.V. All rights reserved. Keywords: Photocatalysis; Titanium dioxide; Nanostructured materials; Titanium tetrachloride 1. Introduction Photocatalytic processes are rapidly developing as poten- tial techniques for the purification of wastewaters [1,2]. Due to its (photo)stability and low cost, the most used photocat- alyst is titanium dioxide [3] but, unfortunately, most of the TiO 2 powders show low values of quantum efficiency [4]. The photoactivity strongly depends on several variables as preparation method, particle size, reactive surface area, ratio between anatase and rutile phases [5,6]. A way to improve the activity of a photocatalyst is to increase its specific surface area and to decrease the size of the particles. TiO 2 nanoparticles have attracted much attention because of the novel electronic and optical properties originating from the quantum confinement [7,8]. By decreasing particle size, ∗ Corresponding author. Tel.: +39 091 6567229; fax: +39 091 6567280. E-mail addresses: dipaola@dicpm.unipa.it (A. Di Paola), palmisano@dicpm.unipa.it (L. Palmisano). the band gap of the semiconductor becomes larger as indi- cated by an absorption shift to shorter wavelengths [9]. The shift of the conduction band to more negative potentials and of the valence band to more positive potentials may favour redox processes that cannot occur in bulk materials [10,11]. TiO 2 nanoparticles have been employed for the pho- todegradation of various noxious species in aqueous systems [12–23] and in gas phase [24–26]. In most cases, the sam- ples have revealed a high photoactivity compared with that of many commercial samples [21–26]. The favourable char- acteristics of the photocatalysts are related to the small size of the crystallites even if in most cases the samples did not consist of discrete nanoparticles but rather of nanostructured particles. The sol–gel method [27,28] is widely employed for the preparation of nanoparticles, due to the inexpensive equip- ment required and the low temperatures involved. The prop- erties of the sol–gel derived samples are strongly dependent not only on the composition, but also on the preparation 0927-7757/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2004.11.048