Chemical Engineering Journal 97 (2004) 241–248 Effects of Pt and Ag on the photocatalytic degradation of 4-chlorophenol and its by-products Mantana Moonsiri a , Pramoch Rangsunvigit a,∗ , Sumaeth Chavadej a , Erdogan Gulari b a The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok 10330, Thailand b Department of Chemical Engineering, The University of Michigan, Ann Arbor, MI 48109, USA Accepted 19 May 2003 Abstract Photocatalytic degradation of 4-chlorophenol (4-CP) was studied using TiO 2 , Pt/TiO 2 , Ag/TiO 2 prepared by the sol–gel methods and Degussa P25 as photocatalysts. The influence of dissolved oxygen on the reaction rate and amounts of intermediate products were determined. In the experiments, a photocatalyst was suspended in the 4-CP solution, which was then irradiated with an 11 W low pressure mercury lamp emitting UV light in 200–280nm window. The results show that, with TiO 2 (sol–gel), the decrease of 4-CP concentration was much faster than that with Degussa P25. In contrast, the reduction rate of total organic carbon (TOC) with Degussa P25 was much higher than that with TiO 2 (sol–gel). The addition of a small amount of either Pt or Ag into TiO 2 (sol–gel) improved the catalyst activity significantly, the highest activity being obtained with 1.0% Pt/TiO 2 and 0.5% Ag/TiO 2 . 0.5% Ag/TiO 2 showed the highest activity in terms of both 4-CP and TOC removals. Hydroquinone (HQ) and hydroxyhydroquinone were identified experimentally as the main intermediate products in the presence of dissolved oxygen. The availability of dissolved oxygen played a significant role in enhancing the photocatalytic degradation of 4-CP for all the catalysts. © 2003 Elsevier B.V. All rights reserved. Keywords: Total organic carbon; Photocatalysts; Hydroquinone 1. Introduction 4-Chlorophenol (4-CP), known as a toxic and non- biodegradable organic compound, is widely used for the production of dyes, drugs, and fungicide [1]. As a result, 4-CP is present in the wastewater of plants. The removal of this compound from wastewaters is currently performed by conventional treatment methods, such as biological treat- ment, chlorination and adsorption. However, the biological process usually requires a considerably long treatment time to break down organic pollutants leading to an unac- ceptable level of 4-CP in the final effluent. Chlorination poses another problem since it often generates carcinogenic by-products. Granular activated carbon adsorption is an- other commercialized process but the spent carbon needs to be disposed [2]. Photocatalytic oxidation has been accepted as a promis- ing alternative to the conventional methods because, with suitable catalysts, most pollutants can be completely miner- ∗ Corresponding author. Tel.: +66-2-218-4135; fax: +66-2-215-4459. E-mail address: pramoch.r@chula.ac.th (P. Rangsunvigit). alized to carbon dioxide in the presence of UV or near-UV illumination. Moreover, this technique does not utilize any additional chemicals and can be operated at room tempera- ture [3]. The photocatalytic process starts with illumination of a photocatalyst that is normally a semiconductor, with light of an appropriate wavelength. Interaction of the cata- lyst, with photons, produces electrons and holes that easily migrate to the catalyst surface and initiate the redox reaction. Although a wide range of catalysts has been tested, titania (TiO 2 ) seems to be the most widely used catalyst because it is stable in most working conditions, corrosion resistant, and relatively inexpensive [4]. It was reported that 4-CP was completely degraded in the presence of TiO 2 and Pt/TiO 2 but the total organic carbon (TOC) still remained at a high level [5]. This was because 4-CP was transformed to other intermediate products rather than carbon dioxide. In this work, we report the results of our investigation of the formation of the intermediate products of photocatalytic degradation of 4-CP using TiO 2 , Pt/TiO 2 and Ag/TiO 2 . Ag/TiO 2 was employed to investigate the possibility of improving the activity of TiO 2 for the decomposition of 1385-8947/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2003.05.003