~ ) Pergamon 0043-1354(93)E0045-T Wat. Res. Vol. 28, No. 8, pp. 1845-1849, 1994 Elsevier ScienceLtd. Printed in Great Britain RESEARCH NOTE PHOTOCATALYTIC DEGRADATION OF PHENOL AND CHLORINATED PHENOLS USING Ag-TiO2 IN A SLURRY REACTOR ROSANA M. ALBERICI and WILSON F. JARDIM* Instituto de Quimica, UNICAMP, CP 6154, 13081-970 Campinas, SP, Brazil (First received July 1992; accepted in revised form November 1993) Abstraet--Photodegradation of phenol (PhOH), 2,4-dichlorophenol (2,4-DCP), 2,3,5-trichlorophenol (2,3,5-TCP) and pentachlorophenol (PCP) was investigated using an open upflow slurry reactor and TiO z (Ag-loaded) as photocatalyst. Light was provided by three 125 W high-pressure mercury lamps. Best degradation rates were obtained using 250 mg 1- ~ of Ag-TiO2 in the presence of H202 and a constant supply of air (l.71min-m). Under this optimized condition, destruction rate constants obtained for a Ix 10-4M solution of PhOH, 2,4-DCP, 2,3,5-TCP and PCP were 0.0493, 0.0430, 0.0367 and 0.0356 min -m, respectively. Each gram of phenol required 1.70 kW for its photodestruction. Key words--photocatalysis, TiO 2, Ag-TiO 2, slurry reactor, hydrogen peroxide, phenol, chlorinated phenols INTRODUCTION Phenolic compounds are common pollutants in industrial effluents. The fate of these compounds is of interest because of their toxicity to humans and to aquatic life. The destruction of these pollutants is therefore a priority. Photocatalytic oxidation is a comparatively recent method for the destructive removal of organic impurities present in waters and wastewaters. A recent report by the National Research Council calls for the US Department of Energy to continue to support fundamental research on water and waste- water oxidative destruction using photocatalysis (C&EN, 1991). Several catalysts such as CdS (Davis and Huang, 1990), et-Fe203 and ZnO (Kormann et al., 1989) and TiO2 (Pruden and Ollis, 1983; Matthews, 1990; Sclafani et al., 1991) have been used for this purpose. Photocatalysis using TiO2 is attractive for many reasons: (a) TiO2 is cheap and non-toxic, (b) it shows good chemical stability over a wide range of pH, (c) it is available in allotropic forms with high photo-activity, (d) it can be coated as a thin film on a solid support and (e) it can be activated by sunlight. Photocatalytic experiments with TiO 2 suspensions, in general, are conducted using a cylindrical annular pyrex batch reactor with an immersed lamp. Such an apparatus exhibits limited capacity (less than I liter) and the suspension is magnetically stirred. *Author to whom all correspondence should be addressed. In this work, the photodegradation of phenol and chlorinated phenols was investigated using an open upflow slurry reactor of 6.31. capacity, illuminated by three immersed high-pressure mercury lamps. The stirring and cooling of the suspension were obtained via recirculation with a peristaltic pump. The miner- lization of phenol and chlorinated phenols was obtained in the presence of Ag-loaded TiO2 (Kondo and Jardim, 1991), H202 and air. EXPERIMENTAL Titanium dioxide (anatase) was supplied by Aldrich, with a surface area of 9.35 m 2 g-i (BET). The method of thermal Ag-loading on TiO 2 has been described previously (Kondo and Jardim, 1991). Phenol and chlorinated phenols were supplied by Aldrich. Hydrogen peroxide (Merck) was used in the photodegradation experiments to enhance the rate reaction. All solutions were prepared with distilled, deionized water. The 6.3 1. open upflow photoreactor was constructed using an acrylic cylinder of 13.5 cm i.d. and 50cm height, as shown in Fig. 1. The illumination was provided by three 125 W high-pressure mercury lamps (Philips HPL-N) with the glass bulb removed, spaced 15cm from each other. Radiant flux at the bulk solution was 35 Wm-2 measured at 365nm by a Radiometer (Cole-Parmer, serie 9811, 365 nm) and using one lamp only. A Vycor tube, that does not absorb u.v. radiation, was used to shield the lamp inside the reactor. Recirculation of the suspension was provided with the help of a peristaltic pump (Flex-FIo, model NO:A-1845V-7N) and the temperature was kept at 25 _+4°C using an ice-bath as heat exchanger. The flow rate of 145ml min -~, corresponding to a hydraulic retention time of 43 min, was selected as the optimal flow for recircu- lation and cooling of the suspensions studied in this work. WR 28/~-L 1845