Synthesis of nanosized biogenic magnetite and comparison of its catalytic activity in ozonation

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 parachlorobenzoic acid (pCBA). XRD and TEM analyses showed that the biogenic iron oxide was magnetite phase (Fe₃O₄) 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.