Photocatalytic degradation of Crystal Violet (C.I. Basic Violet 3) on silver ion doped TiO 2 C. Sahoo, A.K. Gupta * , Anjali Pal * Department of Civil Engineering, Indian Institute of Technology, Kharagpur, India Received 12 July 2004; received in revised form 24 August 2004; accepted 5 September 2004 Available online 26 November 2004 Abstract The photocatalytic degradation of Crystal Violet, a triphenyl methane dye (also known as Basic Violet 3) in aqueous solutions was investigated with Ag C doped TiO 2 under UV and simulated solar light. The dye degradation using untreated TiO 2 and Ag C doped TiO 2 was compared. It was found that Ag C doped TiO 2 is slightly more efficient. Ag C doping was done also to separate the photocatalyst easily from the treated effluent just by settling or centrifuging and decantation thus avoiding the costly filtration process. Measurements of COD were done at regular intervals to have an idea of mineralization of the dye. The effects of pH, catalyst loading, substrate concentration, interfering substances such as Cl ÿ , NO 3 ÿ , SO 4 2ÿ , HPO 4 2ÿ , Ca 2C , Fe 3C and humic acid on dye degradation were investigated. The degradation of the dye (20 ppm) was O97% on UV illumination for 105 min with TiO 2 and O99% with Ag C doped TiO 2 . The dye (20 ppm) was found to degrade about 88% after illumination for 10 h by a simulated solar light source in the presence of Ag C doped TiO 2 . The degradation kinetics fit well to LangmuireHinshelwood rate law. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: TiO 2 ; Ag C doped TiO 2 ; Photocatalytic degradation; Crystal Violet; UV-irradiation 1. Introduction Various industries such as textiles, paint and var- nishes, ink, plastics, pulp and paper and cosmetics use different types of organic dyes and dye intermediates. About 15% of the dyes produced throughout the world are lost during synthesis and processing with wastewater [1,2]. Such coloured dye effluents pose a major threat to the surrounding ecosystem. Some of the dyes are extremely toxic [3]. The increased public concern with these dyes and the stringent international environmental standards (ISO 14001) have prompted the need to develop novel treatment methods for converting these organic dyes to harmless compounds [4]. Dye effluents can be treated by biological methods, flocculation, reverse osmosis, adsorption on activated charcoal, chemical oxidation methods and advanced oxidation processes [5]. Biological methods have been proved to be ineffective [6e8]. Flocculation, reverse osmosis and adsorption methods transfer the pollutants to other media, thus causing secondary pollution [9,10]. Chemical oxidation methods are not cost effective [11]. Advanced oxidation processes have been used to treat various organic pollutants during the last two decades. Among these oxidation processes, heterogeneous photo- catalytic methods are the most effective and attractive ones. They use atmospheric oxygen as oxidant and can be carried out under ambient conditions and may lead to total mineralization of organics to CO 2 , water and low molecular weight fatty acids. Photocatalytic degra- dation of harmful dyes in the presence of the large band * Corresponding authors. Tel.: C91 3222 283 428; fax: C91 3222 255 303. E-mail addresses: agupta@civil.iitkgp.ernet.in (A.K. Gupta), anjalipal@civil.iitkgp.ernet.in (A. Pal). 0143-7208/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2004.09.003 Dyes and Pigments 66 (2005) 189e196 www.elsevier.com/locate/dyepig