Black carbon-mediated reductive transformation of nitro compounds by hydrogen sulfide

The objective of this study is to investigate the fate of redox-sensitive nitro compounds in the presence of black carbon (BC) materials in electron-rich subsurface environments. The ability of various types of BC was examined, including graphite, carbon nanotubes, chemically converted graphene, activated carbon, diesel soot, and biochar, to promote the reduction of 2,4-dinitrotoluene, pendimethalin, and trifluralin by hydrogen sulfide, a naturally occurring reductant, through batch experiments. Compared to removal in sorption control experiments with BC materials and direct transformation with hydrogen sulfide, the presence of BC markedly enhanced the reduction of nitro compounds by hydrogen sulfide, indicating that BC can be an electron-transfer mediator in the presence of hydrogen sulfide. Possible mechanisms and environmental implications of BC-mediated reduction reactions in soils and sediments are discussed.