Removal of explosive compounds RDX and DNAN from water by catalytic ozonation

Abstract

RDX and DNAN are highly energetic explosive compounds that are quite resistant to natural breakdown and decomposition. Hydroxyl radicals have shown appealing application in transforming organic contaminants, providing hope that they can be used to break down explosives contaminants without any harmful byproducts. In this work, the catalytic ozonation process was utilized to generate hydroxyl radicals for the removal of RDX and DNAN from water. Hydroxyl radical formation was facilitated from ozone using as solid catalysts either carbon nanotubes functionalized with carboxyl groups (CNT-COOH) or graphene oxide. Results of RDX and DNAN degradation through this process involvedtwo parts, an adsorption phase to test contaminant adsorption and reaction phase. The adsorption phase included mixing contaminant solutions with and without catalyst for 15 minutes. Reaction phase was marked by bubbling ozone into the solution and taking samples at intervals. Starting at concentration levels of 62 uM, within five minutes of bubbling ozone exposure, the RDX concentrations decreased nearly half to 26 uM with CNT-COOH catalyst present. By the end of the experiment, concentration of RDX had completely been diminished by 41 uM.Ozone alone did not remove RDX. For testing with compound DNAN, a reaction was recorded right away during the adsorption phase. Beginning with around 50 uM, within the first ten minutes of stirring, DNAN concentration levels had already decreased by more than half to 25 uM due to sorption alone. 20 minutes later, at the end of the ozonaiii tion period, DNAN concentration was less than 6 uM when CNT-COOH was present in comparison to only ozone present Rates of RDX and DNAN removal were greater when CNT-COOH was the catalyst compared to graphene oxide. These results indicate that the catalytic ozonation process could be employed to remove aliphatic and aromatic explosive compounds from water, but further experimentation is needed to determine reaction kinetics and water chemistry influences on removal rates. Furthermore, catalyst properties including surface area and surface chemistry should be explored to identify the idealized carbonaceous surface for catalytic ozonation. iv ACKNOWLEDGEMENTS