Available on line at Association of the Chemical Engineers AChE www.ache.org.rs/CICEQ Chemical Industry & Chemical Engineering Quarterly 15 (1) 17−19 (2009) CI&CEQ 17 ANĐELKA TOMAŠEVIĆ 1 JELENA ĐAJA 2 SLOBODAN PETROVIĆ 2 ERNŐ E. KISS 3 DUŠAN MIJIN 2 1 Institute of Pesticides and Environ- ment Protection, Banatska 31b, 11080 Belgrade-Zemun, Serbia 2 University of Belgrade, Faculty of Technology and Metallurgy, Karne- gijeva 4, 11120 Belgrade, Serbia 3 University of Novi Sad, Faculty of Technology, Bul.Cara Lazara 1, 21000 Novi Sad, Serbia SHORT COMMUNICATION UDC 628.316:632.951 A STUDY OF THE PHOTOCATALYTIC DEGRA- DATION OF METHOMYL BY UV LIGHT The photocatalytic degradation of insecticide methomyl in water, using TiO 2 and ZnO (Merck), under UV (366 nm) was studied. The influence of the cata- lyst concentration and pH was investigated. The optimal concentration of the catalyst was found to be 2.0 g/l. It was found that ZnO is a better catalyst than TiO 2 under the same reaction conditions. Also, the influence of NaCl was stu- died. The presence of Cl − significantly affects the photodegradation of the pollutant. Key words: photocatalytic degradation; methomyl; titanium dioxide; zinc oxide. Methomyl (Figure 1) is a broad spectrum insec- ticide. It is a very toxic and hazardous compound and a pollutant of environmental concern because of its high solubility in water (57,9 g/l at 25 °C) [1]. Since the sorption affinity of methomyl to soils is rather low, it can easily cause contamination of both ground and surface water sources [2]. Figure 1. Structure of methomyl. IUPAC name: S-methyl N-(me- thylcarbamoyloxy) thioacetimidate. Although biological processes are often most eco- nomical for a contaminated site cleanup and an in- dustrial waste treatment, the advanced oxidation pro- cesses (AOPs) provide an effective means of rapidly treated compounds with the efficient process control [3]. Methomyl has also been photodegradated by us- ing AOP. A different catalyst has been used, mostly TiO 2 [4-8]. Photo-Fenton reaction was also employed [9]. Corresponding author: A. Tomašević, Center for Pesticides and Environment Protection, Banatska 31b, 11080 Belgrade-Ze- mun, Serbia E-mail: academia@beotel.yu Paper received: October 6, 2008. Paper revised: October 30, 2008. Paper accepted: October 31, 2008. The aim of the present work is to study the pho- tocatalytic degradation of insecticide methomyl in wa- ter using TiO 2 and ZnO (Merck) under UV light (366 nm). The influence of the catalyst concentration, pH and NaCl concentration was studied. EXPERIMENTAL Hydrochloric acid, sodium chloride and sodium hydroxide (all p.a.) were obtained commercially. TiO 2 , Merck Eusolex ® T (anatase modification), and ZnO (Merck) were used as received. Methomyl was ob- tained from DuPont (analytical grade, 99.8 %). Deio- nised water was obtained from a Milipore Waters Milli Q purification unit. Irradiations under UV light (366 nm) were per- formed in an open flask made of a quartz glass (20 ml volume) with the UV lamp (2x8 W) placed 5 cm from the surface of the reaction mixture. The photodegradation of methomyl was studied by preparing a solution containing 16.4 mg/l of metho- myl and a certain amount of the catalyst. In a typical experiment, 15 ml of the solution was used. Then, the lamp was switched on and during the irradiation the agitation was applied, and after an appropriate time of irradiation the suspension was sampled. The reaction mixtures were kept at 20 °C. The concentration of me- thomyl was determined after the centrifugation of a sample by UV-Vis spectrophotometer (Shimadzu 1700)