Carbon tetrachloride transformation on the surface of nanoscale biogenic magnetite particles.
Iron-reducing conditions in subsurface environments promote dechlorination reactions via both biotic and abiotic pathways, the latter often mediated via biologically activated minerals formed by dissimilatory iron-reducing bacteria (DIRB). Here we report the major products and pathways associated with the abiotic transformation of carbon tetrachloride (CT) by nanoscale biogenic magnetite/maghemite particles produced by the DIRB Geobacter metallireducens. Product formation and free radical/carbene trapping studies indicate that CT transformation occurs via three parallel pathways. The first pathway (hydrogenolysis) results in the formation of chloroform (45-50%) via a trichloromethyl free radical (*CCl3) and possibly a trichloromethyl carbanion (**CCl3-). The second and third pathways involve a dichlorocarbene intermediate (**CCl2), which either hydrolyzes to form CO (approximately 38%) (carbene hydrolysis), or undergoes further reduction to yield methane (8-10%) (carbene reduction). The mechanism of methane formation from **CCl2 is not known, but is speculated to involve a sequence of surface coordinated carbenoid and free radical complexes. The large fraction of relatively benign products formed by the carbene-mediated pathways suggests that magnetite/maghemite particles may have a beneficial application in the remediation of CT contaminated environments.
Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan 48109-2125, USA. mmccormi@hamilton.edu
Michael L
ML
McCormick
Peter
P
Adriaens
D002251:Carbon Tetrachloride / Q000737:chemistry*; D052203:Ferrosoferric Oxide; D005609:Free Radicals / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D008697:Methane / Q000032:analysis; D010087:Oxides / Q000737:chemistry*; D010316:Particle Size; D012989:Soil Pollutants / Q000032:analysis*; D012997:Solvents / Q000737:chemistry*; D014873:Water Pollutants / Q000032:analysis*
D005609:Free Radicals; D010087:Oxides; D012989:Soil Pollutants; D012997:Solvents; D014873:Water Pollutants; D002251:Carbon Tetrachloride; D007501:Iron; D008697:Methane; D052203:Ferrosoferric Oxide