105 Bulgarian Chemical Communications, Volume 45, Special Issue B (pp. 105-109) 2013 XPS investigation on the surface of ZnO photocatalytic films obtained by polymer modified spray pyrolysis M. G. Shipochka * , I. D. Stambolova, V. N. Blaskov, P. K. Stefanov Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev St., bl.11, 1113 Sofia, Bulgaria. Received October 17, 2013; Revised November 25, 2013 Photocatalytically active ZnO nanosized films were deposited by polymer modified spray pyrolysis method. The influence of the polymers and the type of zinc precursor on the chemical composition, surface morphologies and the photocatalytic properties towards Malachite Green dye degradation were investigated. The amount of oxygen in the lattice (O L ) and oxygen total (O T ) as well as the atomic ratio of Zn/O T were evaluated by means of X-ray Photoelectron Spectroscopy (XPS). The ZnO films are non-stoichiometric. The addition of polymers to both zinc salt solutions does not change significantly the oxygen concentration in the films. After photocatalytic test the ratio O L /O T decreases, showing that the amount of adsorbed hydroxyl groups is increased. The films obtained from zinc acetate possess higher photocatalytic activity than those, obtained from zinc nitrate. The highest efficiency is achieved with the films obtained from zinc acetate with ethylcellulose addition. Keywords: ZnO, thin films, XPS surface analysis, spray pyrolysis, photocatalytic properties INTRODUCTION The growth of the world’s industry and population has increased the demand for water supply. The textile industries are among the industries that consume largest volumes of water in the processing operations including pre-treatment, dyeing, pattern printing and finishing. It has been reported that some of the dyes used in this industry are toxic, mutagenic and carcinogenic [1]. In general, photocatalysis is used as a pre-treating step to degrade non-biodegradable organic pollutants to biodegradable compounds. As a well-known photocatalyst, ZnO has received much attention in the degradation and complete mineralization of environmental pollutants [2]. The spray pyrolysis process, as a simple and easy thin films deposition method is one of the versatile methods to prepare thin nanosize films. The studies on the ZnO sprayed films surface by XPS analysis before and after pfotocatalysis are quite scarce in the available literature. This information is important because it elucidates the changes on the surface of the photocatalysts. Data about the effects of the polymeric modifier, added to the spray solution composition, and the nature of the zinc precursor in regard to the effectiveness of tuning of some physicochemical characteristics of the ZnO films and their correlations with the catalysts efficiency are quite a few. In this paper we aimed at obtaining correlations between the type of polymer additive in the zinc precursor spray solution, some physicochemical characteristics and the photocatalytic properties of the ZnO films. EXPERIMENTS Two types of zinc precursor solutions have been prepared for the purpose of spray pyrolysis deposition. Zinc acetate (Zn(CH 3 COO) 2 ) and zinc nitrate (Zn(NO 3 ) 2 ) were diluted in an ethanol–water mixture to obtain 0.4 M/L solutions of Zn and these were denoted as “sol A” and “sol B”, respectively. The ethanol-water volume ratio in the solutions was 3:1. Polyvinyl alcohol (PVA) was prepared in ethanol-water mixture under stirring (sol C). A defined quantity of “sol C” was added to sols A or B in order to prepare the final spray solutions with 30 wt% PVA. The obtained solutions were denoted as “sol AC” and “sol BC”, respectively. In parallel to this the solution of ethyl cellulose [C 6 H 7 O 2 (OC 2 H 5 ) 3 ] n in ethanol was prepared under stirring for 2h (sol D) (40wt%) and then added to “sol A” and “sol B” in order to obtain the final solutions “sol AD” and “sol BD”. The aerosol was transported to the aluminum foil plates heated at © 2013 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria * To whom all correspondence should be sent: E-mail: shipochka@svr.igic.bas.bg