Synthesis of nanosized biogenic magnetite and comparison of its catalytic activity in ozonation Haeryong Jung 1 , Jung-Woo Kim, Heechul Choi *, Ji-Hoon Lee, Hor-Gil Hur Department of Environmental Science and Engineering, Gwangju Institute of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712, South Korea 1. Introduction It has been clearly demonstrated that metal catalysts can effectively be utilized to improve the ozonation efficiency for the removal of a number of organic compounds [1,2]. In particular, solid metal oxides are more useful in catalytic ozonation than ionized metals, as ionized metals are considered toxic substances in water. Beltran et al. [3] further reported that ozone efficiency in heterogeneous catalytic ozonation was higher than that found in homogeneous catalytic ozonation. Our previous work also indicates that heterogeneous catalytic ozonation using microsized FeOOH enhances the degradation of ozone and para-chlorobenzoic acid ( pCBA) [1]. Iron oxides and hydroxides have been used in the catalytic ozonation due to advantages, such as their abundance on earth and their stable form [4]. These materials represent 6% of the chemical composition of the Earth’s crust [5]. Specifically, nanosized iron oxides are drawing a great deal of attention in chemical and biological processes because of following reasons: (1) nanosized particles have larger surface area/volume ratios than bulk materials for a given amount; and (2) the structure of the nanosized iron oxide surface may differ from those of bulk materials. Hence, reducing the diameter of iron oxides to nanometer size could enhance the reactivity. Nanosized iron oxides have been synthesized by using various synthesis methods, such as electrochemical, sol–gel, and thermal decomposition methods; however, these methods generally use toxic and expensive chemicals as reactants or complex devices or high-energy cost. For example, the thermal decomposition method requires toxic organic solvents and surfactant to be heated up to 320 8C, producing toxic wastes during the process. To this extent, the biomineralization could be considered as an effective alternative for the synthesis of nanosized iron oxide, as it is both environmentally friendly and cost-effective. Specifically, magne- tite (Fe 3 O 4 ) can be formed by a diversity of organisms; here two different types of biogenic magnetite are reported: biologically induced magnetite and biologically controlled magnetite. Biolo- gically controlled magnetite is a biomineral comprised of highly ordered crystals, whereas biologically induced magnetite is extracellularly produced biomineral that does not crystallize under strict genetic control [6]. The amount of biologically controlled magnetite produced is very small, because it is synthesized within microorganisms. For this study, we synthesized Applied Catalysis B: Environmental 83 (2008) 208–213 ARTICLE INFO Article history: Received 17 July 2006 Received in revised form 14 February 2008 Accepted 19 February 2008 Available online 26 February 2008 Keywords: Biogenic iron oxide Magnetite Ozonation Catalytic reaction pCBA ABSTRACT Nanosized biogenic iron oxide was synthesized by dissimilatory iron-reducing bacterium, Shewanella sp. This biogenic iron oxide was evaluated as a catalyst in the heterogeneous catalytic ozonation of para- chlorobenzoic acid ( pCBA). XRD and TEM analyses showed that the biogenic iron oxide was magnetite phase (Fe 3 O 4 ) and was composed of nanosized irregular particles in the range of 10.0  4.0 nm in diameter. Catalytic ozonation was carried out at acidic pH levels (2.5) in the presence of the biogenic magnetite. It was clearly shown that the biogenic magnetite enhanced the degradation of pCBA by the production of  OH resulting from the catalytic decomposition of ozone on the surface of the particles. Functional groups on the surface of the biogenic magnetite played a role of catalytic active sites, and this was confirmed by FT-IR and titration analyses. However, the biogenic magnetite showed a lower catalytic efficiency than the commercial nanosized magnetite, resulted from the formation of 4 times bigger aggregates of the biogenic magnetite than the commercial one in aqueous solutions. The R ct values representing the ratio of hydroxyl radicals and ozone were found to be divided into two regions during reaction. The R ct values during first period (1 min) were much greater than those during second period, and this was caused by initial rapid decrease of pCBA. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +82 62 970 2441; fax: +82 62 970 2434. E-mail address: hcchoi@gist.ac.kr (H. Choi). 1 Present address: Radwaste Disposal Research Team, Nuclear Engineering & Technology Institute (NETEC), Korea Hydro & Nuclear Power Co. LTD., 25-1 Jang- dong, Yuseong-gu, Daejeon 305-343, South Korea. Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb 0926-3373/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2008.02.016