Decomposition of perfluorocarboxylic acids (PFCAs) by heterogeneous photocatalysis in acidic aqueous medium Sri Chandana Panchangam, Angela Yu-Chen Lin, Khaja Lateef Shaik, Cheng-Fang Lin * Graduate Institute of Environmental Engineering, National Taiwan University, 71-Chou-shan Road, Taipei 106, Taiwan, ROC article info Article history: Received 5 June 2009 Received in revised form 8 July 2009 Accepted 9 July 2009 Available online 8 August 2009 Keywords: Perfluorodecanoic acid Perfluorononanoic acid Perfluorooctanoic acid Photocatalysis Mineralization Perchloric acid abstract Decomposition of perfluorocarboxylic acids (PFCAs) is of prime importance since they are recognized as persistent organic pollutants and are widespread in the environment. PFCAs with longer carbon chain length are particularly of interest because of their noted recalcitrance, toxicity, and bioaccumulation. Here in this study, we demonstrate efficient decomposition of three important PFCAs such as perfluoro- octanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) by heteroge- neous photocatalysis with TiO 2 as a photocatalyst in acidic aqueous solutions. The PFCAs were decomposed into shorter carbon chain length PFCAs and fluoride ions. Photoholes of excited TiO 2 gener- ated upon UV-irradiation are found to be the oxidation sites for PFCAs. Therefore, creation and sustenance of these photoholes in the acidic aqueous medium has enhanced the decomposition of PFCAs. Heteroge- neous photocatalytic treatment achieved more than 99% decomposition and 38% complete mineralization of PFOA in 7 h. The decomposition of other PFCAs was as high as 99% with a defluorination efficiency of 38% for PFDA and 54% for PFNA. The presence of perchloric acid was found to enhance the decomposition by facilitating the ionization of PFCAs. The oxygen present in the medium served both as an oxidant and an electron acceptor. The mechanistic details of PFCA decomposition and their corresponding minerali- zation are elaborated. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Perfluorochemicals (PFCs) are a set of anthropogenic fluorinated organic compounds with a wide range of applications (Key et al., 1997; Prevedouros et al., 2006). PFCs resist several conventional treatment processes in the drinking water (Skutlarek et al., 2006) and wastewater treatment plants (Schultz et al., 2006). The higher resistance of PFCs to treatment is attributed to the extreme stabil- ity offered by the extremely strong carbon–fluorine bonds, the very same characteristic that makes it an important constituent for var- ious commercial and industrial applications such as surface-treat- ment, surfactant, and fire retardant. Perfluorocarboxylic acids (PFCAs) are a subset of PFCs with a characteristic carboxylic group at a terminal end for a train of perfluorinated carbon atoms with varying lengths (Fig. 1). PFCAs with a perfluorinated carbon chain length n P 7 have been found in different environmental media with water being a predominant matrix (Prevedouros et al., 2006; Zushi et al., 2008; Lin et al., 2009b; Murakami et al., 2009). The toxicity (Hekster et al., 2003; Lau et al., 2004) and bioaccumu- lation of PFCAs have been reported and suggested that the PFCAs with a longer carbon chain length (n P 7) are more bioaccumula- tive (Conder et al., 2008). The eco-friendly abatement technologies of PFCAs are therefore imperative in view of their great environ- mental concern. Recently, a significant research interest on treatment of PFCs containing water followed the appearance of few peer-reviewed publications on the decomposition of PFCAs. Predominantly the treatment technologies consisted of either photochemical ap- proaches (Hori et al., 2003a,b, 2004a,b) or sonochemical treatment (Moriwaki et al., 2005; Cheng et al., 2008; Vecitis et al., 2008). Photochemical oxidants such as persulfate (Hori et al., 2005), or photocatalysts such as heteropolyacid (Hori et al., 2003a,b, 2004a,b) have been used to decompose PFCAs under UV-irradia- tion. These studies suggested that the electron transfer seems to facilitate the PFCA decomposition by photochemical approaches (Hori et al., 2004a, 2005; Chen and Zhang, 2006). Heterogeneous photocatalysis with TiO 2 is an effective method for the treatment of various organic contaminated waters including halogenated organics (Hoffmann et al., 1995; Gaya and Abdullah, 2008). TiO 2 is a widely used photocatalyst because of its availability, non-tox- icity, chemical and biological stability, photo-stability and low cost (Hoffmann et al., 1995; Kabra et al., 2004; Gaya and Abdullah, 2008). Recently, TiO 2 -mediated photocatalysis has shown to decompose heptafluorobutanoic acid (Dillert et al., 2007) and per- fluorooctanoic acid (PFOA) (Panchangam et al., 2009) to certain 0045-6535/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2009.07.003 * Corresponding author. Tel.: +886 2 23627427; fax: +886 2 23928830. E-mail address: cflin@ntu.edu.tw (C.-F. Lin). Chemosphere 77 (2009) 242–248 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere