Immobilisation of TiO 2 powder for the treatment of polluted water J.A. Byrne * , B.R. Eggins, N.M.D. Brown, B. McKinney, M. Rouse School of Applied Biological and Chemical Sciences, University of Ulster at Jordanstown, Newtownabbey BT37 0QB, Ireland Received 27 July 1997; received in revised form 26 October 1997; accepted 17 November 1997 Abstract TiO 2 powder was immobilised on solid support substrates (stainless steel, titanium alloy, titanium metal, and tin oxide coated glass) using electrophoretic coating and spray coating. Electrochemical anodisation of titanium metal was also carried out to give a thin ®lm of TiO 2 on the surface. The coated substrates were annealed in air at elevated temperatures to improve the adhesion of the catalyst to the supporting substrates. The photocatalytic ef®ciency of the TiO 2 coatings was compared using the degradation of phenol in aqueous solution as a standard test system. In the case of the powder derived ®lms, the photocatalytic ef®ciency was found not to be markedly dependent upon either the substrate used or the annealing temperature employed in the coating process. Surface analysis of the immobilised TiO 2 showed no signi®cant differences in the elemental composition or in band gap energies. The electrophoretic coating method was found to be the most reproducible resulting in highly fractured thick ®lms with high photocatalytic activity. # 1998 Elsevier Science B.V. Keywords: Titanium dioxide; Immobilisation; Photocatalysis; Water treatment 1. Introduction TiO 2 photocatalysis is a possible alternative to conventional water treatment technologies. When TiO 2 is illuminated with light of <400 nm, an elec- tron is promoted from the valence band to the con- duction band of the semiconducting oxide to give an electron/hole pair. The valence band potential is posi- tive enough to generate hydroxyl radicals at the sur- face and the conduction band potential is negative enough to reduce molecular O 2 . The hydroxyl radical is a powerful oxidising agent and attacks organic pollutants present at or near the surface of the TiO 2 resulting usually in their complete oxidation to CO 2 . The mechanisms of photocatalysis are discussed in recent reviews by Mills et al. [1], Hoffmann et al. [2], and Fox and Dulay [3]. The use of TiO 2 in suspension is ef®cient due to the large surface area of catalyst available for reaction. Some workers have developed pilot scale treatment systems employing TiO 2 as an aqueous suspension [4,5]. If the TiO 2 is used in a suspension reactor, the catalyst must be removed following the treatment. Post-treatment removal requires a solid liquid separa- tion stage which adds to the overall capital and run- ning costs of the plant. Alternatively, the catalyst may be immobilised onto a suitable solid support matrix which would eliminate the need for post-treatment removal. When the catalyst is immobilised, there is inher- ently a decrease in the surface area available for Applied Catalysis B: Environmental 17 (1998) 25±36 *Corresponding author. Tel.: +44 1232 366 113; fax: +44 1232 366 812; e-mail: j.byrne@ulst.ac.uk 0926-3373/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0926-3373(97)00101-X