Effect of sample preparation and humidity on the photodegradation rate of CEES on pure and Zn doped anatase TiO 2 nanoparticles prepared by homogeneous hydrolysis Lars O ¨ sterlund a, *, Va ´clav S ˇ tengl b , Andreas Mattsson a , Snejana Bakardjieva b , Per Ola Andersson a , Frantis ˇek Oplus ˇtil c a FOI CBRN Defence and Security, SE-901 82 Umea ˚, Sweden b Institute of Inorganic Chemistry AS CR v.v.i., 250 68 R ˇ ezˇ, Czech Republic c Military Technical Institute of Protection Brno, Veslarˇska ´ 230, 637 00 Brno, Czech Republic 1. Introduction Photocatalytic decomposition of pollutants on wide band gap semiconducting metal oxides and in particular TiO 2 nanoparticles is a promising remediation technology, which has advanced significantly during the past two decades [1–6]. Several authors have reported the use of TiO 2 for photocatalytic degradation of toxic chemicals, including chemical warfare agents (CWA) [7–9]. The latter is interesting since available decontamination technol- ogy suffers from several disadvantages such as large volume of degassing solutions or toxic by-products, which require post- treatment methods. Several problems have however been encountered when evaluating the efficiency of TiO 2 for CEES degradation including build up of inorganic sulphur on the catalyst surface and gradual deterioration of the activity which necessitates catalyst regeneration [7,8]. In view of the hazards of CWA, simile agents with similar chemical properties are usually employed in research. 2-Chlor- oethyl ethyl sulfide (CEES) is a simile substance for sulphur mustard gas, HD (2,2-dichloroethyl sulfide). It possesses both S- group and Cl-group functionality which makes its chemistry more complex than simile molecules containing single reactive groups, e.g. opening up competing pathways for charge transfer. It has recently been reported that electron transfer from the TiO 2 conduction band occurs only into the Cl-group [10]. Considerable efforts have been exerted to develop new and cost-effective preparation methods of titania and doped titania with enhanced photocatalytic properties [6,11,12]. Homogeneous Applied Catalysis B: Environmental 88 (2009) 194–203 ARTICLE INFO Article history: Received 30 May 2008 Received in revised form 19 September 2008 Accepted 26 September 2008 Available online 9 October 2008 Keywords: CEES TiO 2 Photocatalysis Homogeneous hydrolysis Diffuse reflectance Fourier transform infrared spectroscopy ABSTRACT Pure titania and titania doped with Zn 2+ were prepared by homogeneous hydrolysis in aqueous solution with urea and thioacetamide as precipitating agents. The materials were characterized by XRD, TEM, BET and BJH analysis, which show microporous, nanaocrytsalline anatase phase titania in the size range 4– 5 nm and specific surface area 200–500 m 2 /g. Adsorption and photocatalytic decomposition of 2- chloroethyl ethyl sulfide (CEES) was measured on dry and water pre-covered titania surfaces, respectively. Illumination with UV light leads to rapid decomposition of CEES on all samples resulting in formation of surface bound ethoxy, chloro ethoxy, aldehydes, acetone and carboxylates. Volatile sulphur moieties (S O) and isocyanate (Ti-NCO) are observed which is related to the synthesis methods employed. A procedure for removing residual synthesis products from the particles was devised and the intrinsic photodegradation rate was determined on the purified samples and compared with the as prepared samples. The photodegradation rate is notable higher for the purified TiO 2 nanoparticles prepared by the urea route with respect to the ‘‘as prepared’’. In the case of the Zn doped TiO 2 samples a diminution in photodegradation rate is observed after purification. The results are correlated with the amount of volatile residual synthesis products present on the different particles. All materials have comparable or higher photo-reactivity than P25 (Degussa). On a humidified surface, the effects from synthesis residues, in particular volatile sulphur moieties, are reduced due to reactions with water and improved photoreaction rates for all samples are observed. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +46 90 106900; fax: +46 90 106800. E-mail address: lars.osterlund@foi.se (L. O ¨ sterlund). Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb 0926-3373/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2008.09.029