Nanoparticulate cerium dioxide and cerium dioxide–titanium dioxide composite thin films on glass by aerosol assisted chemical vapour deposition Uzma Qureshi, Charles W. Dunnill, Ivan P. Parkin * Materials Chemistry Research Centre, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK 1. Introduction Designing composite systems with embedded nanoparticles is known to enhance the properties of the host matrix [1–4]. Nanoparticles are extensively investigated because of their unique electronic and optical properties which can substantially differ from those of the bulk materials. Much effort has been devoted to the synthesis and characterisation of stable dispersions of nanoparticles, particularly silver, gold and other noble metals [4] with intended application in a broad range of areas such as photography, catalysis, biological labelling, photonics, optoelec- tronics and surface enhanced Raman scattering detection [5]. When tailoring the properties of semiconductor films by the incorporation of nanoparticles into the host matrix the size and shape of the nanoparticles as well as the mode of deposition is important [6]. If the deposition or processing temperature is too high the nanoparticles have a natural tendency to agglomerate into larger units and thereby reduce their surface free-energy or react with their surroundings, loosing the functional properties largely associated with particle size. Methods have been devised to avoid these problems including surface passivation with molecular protecting groups or to incorporate into a host matrix that lends stability such as a nanoparticle–polymer composite [7]. The nanoparticles can be prepared by many methods including: condensation in the vapour phase, chemical reduction in the solution phase, photon or ultrasound induced reduction, as well as electrostatic spraying on solid substrates [1,7]. Cerium oxide (CeO 2 ) is frequently incorporated into oxidation catalysts as it is known to enhance the catalytic combustion of hydrocarbons and carbon monoxide. It is an n-type semiconductor with a band-gap of 2.9–3.2 eV [8,9] that can be photo-activated by irradiation with light in the near UV-region. It has the potential therefore to be used as a practical photocatalyst for the oxidation of pollutants [2], however there seems to be some disagreement in the literature with some reports suggesting that cerium dioxide shows no activation while others show that it operates as a superior photocatalysts to titania [8–10]. It seems that both the specific analyte tested for the degradation studies and the form of the cerium oxide, plays a critical role as to whether it will function as a photocatalyst. CeO 2 powders have recently been found to be a good visible light catalyst for the degradation of azodyes [9], eluding to the potential application for film technology in the purification of water. CeO 2 has also been suggested for use as a water splitting photocatalyst for the formation of oxygen [8]. Titanium dioxide, especially in the anatase form is the most widely reported photocatalysts [7] and is used in a wide range of self- cleaning applications on a range of substrates including glass (Pilkington Activ TM [11], Saint Gobain BIOCLEAN TM [12], PPG Sunclean [13]), tile (TOTO hydrotech), and steel. We have shown previously that titiania films with embedded nanoparticles can be made by aerosol assisted chemical vapour deposition [14]. In this paper we focus on two specific materials, cerium dioxide and a cerium dioxide/titanium dioxide composite. The films were formed in a standard AACVD process using preformed nanoparticles of CeO 2 dissolved in deionised water, Applied Surface Science 256 (2009) 852–856 ARTICLE INFO Article history: Received 17 February 2009 Received in revised form 18 August 2009 Accepted 20 August 2009 Available online 27 August 2009 Keywords: Cerium dioxide Chemical vapour deposition Photocatalyst Hydrophilic ABSTRACT Two series of composite thin films were deposited on glass by aerosol assisted chemical vapour deposition (AACVD)—nanoparticulate cerium dioxide and nanoparticulate cerium dioxide embedded in a titanium dioxide matrix. The films were analysed by a range of techniques including UV–visible absorption spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive analysis by X-rays. The AACVD prepared films showed the functional properties of photocatalysis and super- hydrophilicity. The CeO 2 nanoparticle thin films displaying photocatalysis and photo-induced hydrophilicity almost comparable to that of anatase titania. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +44 0207 679 4669. E-mail address: i.p.parkin@ucl.ac.uk (I.P. Parkin). Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc 0169-4332/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2009.08.074