Materials Chemistry and Physics 124 (2010) 1225–1231 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Photocatalytic degradation activity of titanium dioxide sol–gel coatings on stainless steel wire meshes M. Bestetti a,∗ , D. Sacco a , M.F. Brunella a , S. Franz a , R. Amadelli b , L. Samiolo b a Politecnico di Milano, Dipartimento di Chimica, Materiali e Ingegneria Chimica, Via Mancinelli 7, 20131 Milano, Italy b Istituto per la Sintesi Organica e la Fotoreattività (ISOF-CNR) c/o Dipartimento di Chimica dell’Università di Ferrara, Via Borsari 46, 44100 Ferrara, Italy article info Article history: Received 12 January 2010 Received in revised form 13 May 2010 Accepted 18 August 2010 Keywords: Titanium dioxide Sol–gel deposition Wire meshes Photocatalysis Environment abstract Stainless steel wire meshes have been functionalised with multiple titanium dioxide (TiO 2 ) coatings deposited by the sol–gel technique, using titanium isopropoxide as precursor and titanium dioxide nanopowders dispersed in the colloidal solution. After the thermal conversion of the amorphous frac- tion of the coating into anatase, the functionalised stainless steel wire meshes were tested for the UV photodegradation of aqueous solutions of methylene blue, solid stearic acid and nitrogen oxides in air. The addition of TiO 2 nanopowders in the colloidal deposition solution enhanced the photocatalytic per- formance of the deposited TiO 2 layers in all the tested conditions. Moreover, increasing the number of coatings (from 1 to 4) improves the photocatalytic efficiency. The catalyst did not show reduced photoreactivity after four repeated cycles in water decontamination from methylene blue, and after up to 10 repeated cycles in nitrogen oxides photodegradation. Complete regeneration of the catalyst could be achieved by rinsing it with warm deionised water and was observed in the case of experiments for NO x abatement. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The global industrial development calls for ever increasing energy consumption and resources and, at the same time, it is a source of severe pollution. This has become a major social issue and several strategies have been proposed aiming at environment remediation. Among the advanced oxidative depollution methods current employed, photocatalysis at semiconductors and at TiO 2 , in particular, has gained considerable attention, as witnessed by a large body of research published in this field in recent years. The discipline is heading fast toward applications in the field of abate- ment of water [1] and air pollutants [2,3]. Recently, an International Standard has been published on a test method for the determina- tion of the air-purification performance of materials that contain or are coated with photocatalyts, such as TiO 2 [4]. The test consists in the photodegradation of nitrogen oxides, which are among the major pollutants in indoor environment, where people generally spend over 80% of their life-time [5], causing serious respiratory problems [6]. TiO 2 -based photocatalyts can be used in the form of either sup- ported thin films or dispersed nanopowders [7]. In the latter case, a great advantage arises from the high surface area of the nanopow- ∗ Corresponding author. Tel.: +39 02 2399 3166; fax: +39 02 2399 3180. E-mail address: massimiliano.bestetti@polimi.it (M. Bestetti). ders, which makes the TiO 2 dispersed in the contaminated fluid in good contact with the pollutants. On the other hand, the use of dispersed nanopowders requires filtering operations at the end of the decontamination process and there is a limit in the TiO 2 nanopowder concentration since high concentration values result in UV light shadowing. On the contrary, despite the limited surface area compared to the dispersed nanoparticles form, supported TiO 2 thin films do not require any further filtering post-treatment of the decontaminated fluid and there is no risk of light shadowing in the design of the most suitable reactor. Supported TiO 2 thin films can be obtained by means of sev- eral methods, such as anodic oxidation [8–15], PVD, sputtering [16] and sol–gel deposition. An exhaustive review on the major synthesis methods was published by Carp et al. [7]. The sol–gel deposition method offers a number of advantages compared to the other deposition techniques: (i) it can be done on a variety of substrate materials; (ii) it can be carried out using an ordinary lab- oratory equipment; (iii) it allows to uniformly coat high contact areas and complex shapes; (iv) the properties of the resulting film can be easily controlled by tuning the deposition parameters; and (v) doping elements can be easily co-deposited. The photocatalytic activity of the TiO 2 sol–gel coating can be improved by carefully choosing the experimental conditions such as controlling the film thickness [17], adhesion to the substrate and surface area [18]. For example, it was demonstrated that the addition of TiO 2 nanoparticles to the sol results in thicker films having good hardness and adhesion to the substrate [19,20]. These 0254-0584/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2010.08.062