Chemical Engineering Science 58 (2003) 679–685 www.elsevier.com/locate/ces Anovellaponiteclay-basedFenanocompositeanditsphoto-catalytic activityinphoto-assisteddegradationofOrangeII JiyunFeng a ,XijunHu a ; * ,PoLockYue a ,HuaiYongZhu b ,GaoQingLu b a Department of Chemical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong b Department of Chemical Engineering, University of Quennsland, Brisbane, Qld 4702, Australia Abstract AnovellaponiteRDclay-basedFenanocomposite(Fe-Lap-RD)hasbeensuccessfullysynthesizedthroughareactionbetweenasolution of iron salt and an aqueous dispersion of laponite RD clay. The X-ray diraction (XRD) results reveal that the Fe-Lap-RD mainly consists of Fe2O3 (maghemite) and Fe2Si4O10(OH)2 (iron silicate hydroxide), which have tetragonal and monoclinic structures, respectively, and has a high specic surface area as well as a high pore volume. The photo-catalytic activity of the Fe-Lap-RD was examined in the photo-assisted degradation of an organic azo dye Orange II. It was found that the mineralization of Orange II undergoes a slower kinetics than discoloration, and 70% total organic carbon (TOC) of 0:2 mM Orange II can be removed in 90 min, implying that the Fe-Lap-RD exhibited a high photo-catalytic activity in the presence of H2O2 and UV light (254 nm) in the photo-assisted degradation of Orange II. In addition, our experiments also illustrate that the Fe-Lap-RD has a long-term stability but is of low cost. This study illustrates the possibility of photo-assisted degradation of organic compounds without the requirements to remove the Fe ions after reaction. Two possible catalytic reaction mechanisms are also proposed. ? 2003 Elsevier Science Ltd. All rights reserved. Keywords: Fe nanocomposite; Photo-assisted Fenton degradation; Pollution; Stability; Environment; Leaching 1. Introduction Inrecentyears,manystudieshavebeenperformedonthe photo-assisted Fenton degradation of organic compounds due to its importance in academic area as well as practi- cal applications in environmental engineering (Pignatello, 1992; Pignatello&Sun,1993; Halmann,1996).Thebiggest disadvantage of homogeneous photo-Fenton process, how- ever,istheremovalofthesludgecontainingmetalssuchas Fe ions at the end of the wastewater treatment. The sludge isusuallytreatedbyprecipitationandre-dissolutionthatare costly and need large amount of chemicals and manpower. To eliminate this drawback, some eorts have been made to develop heterogeneous catalysts such as Naon-based catalysts (Fernandez, Bandara, Lopez, Albers, & Kiwi, 1998; Fernandez, Bandara, Lopez, Buar, & Kiwi, 1999; Fernandez, Djananjeyan, Kiwi, Senuma, & Hilborn, 2000; Bossmann et al., 2001; He,Tao,Ma,&Zhao,2002). How- ever,itshouldbepointedoutthattheNaon-basedcatalysts * Corresponding author. Tel.: +852-2358-0054; fax: +852-2358-7134. E-mail address: kexhu@ust.hk (X. Hu). have two main drawbacks. The rst is their low catalytic activity.Forexample,whenFe 3+ = Naonlmwasusedasa catalyst in the photo-assisted degradation of Orange II, the mineralizationoftheOrangeIIneedsalongtimeupto7h and undergoes a much slower kinetics than the Orange II disappearance,indicatingthatlonger-livedintermediatesare formed in the solution (Fernandez et al., 1998, 1999). Fur- thermore,thelonger-livedintermediatescouldbemoretoxic thantheoriginaldye.Thesecondisthattheyaretooexpen- sive to be used in a practical industrial application. Hence, it is necessary to develop heterogeneous photo-Fenton cat- alysts with high activity but a low cost. Pillared clay materials have been used as catalyst sup- ports because of their particular properties and structures as wellastheirabundanceandlowcost(Burch,1988; Mitchel, 1990; Galarneau, Barodawalla, & Pinnavaia, 1995; Wang, Zhu, & Lu, 1998; Zhu & Lu, 2001). When they are dis- persedinwater,theyswellsignicantlyowingtothehydra- tionoftheinter-lamellaecationswhichactascounterionsto balance the negative charges of the clay layers. Therefore, inorganic polycations in aqueous solutions can be interca- lated into the interlayer gallery by cation exchange. During subsequent heating to a high temperature, the intercalated 0009-2509/03/$-see front matter ? 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0009-2509(02)00595-X