Graphite- and soot-mediated reduction of 2,4-dinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine

Black carbon (BC) is an important class of geosorbents that influence the fate and transport of organic pollutants. It is commonly assumed that molecules sorbed to BC are chemically inert. Here we show that this is not true for redox-sensitive sorbates such as nitro-aromatic compounds. In the presence of graphite or n-hexane soot as a BC material, the reduction of 2,4-dinitrotoluene (DNT) to 2,4-diaminotoluene by dithiothreitol was greatly accelerated. The para and ortho nitro groups of graphite or soot-sorbed DNT had an approximately equal probability of being reduced. This (1:1) regio-selectivity is different from that when DNT is reduced in homogeneous solution. That is, sorption to BC altered both the kinetics and pathway of DNT reduction. Transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine, a nonaromatic nitro compound, by dithiothreitol was also enhanced by graphite, with concurrent formation of formaldehyde. We propose that BC can catalyze the reduction of nitro compounds because it contains microscopic graphitic (graphene) domains, which are both sorption sites and electron conductors. The environmental significance and potential applications of these findings are discussed.