Indirect Oxidation of RDX, HMX, and CL-20 Cyclic Nitramines in Aqueous Solution at Boron-Doped Diamond Electrodes

Abstract

Environmental Context. Nitramine explosives, including RDX, HMX, and the more newly developed CL-20, are the source of groundwater contamination (‘pinkwater’) especially around military installations. These materials all possess an abundance of nitro (NO2) groups, which, like synthetic organohalogens, render them resistant to biodegradation and thereby allows them to persist in the soil and waters. In this study it was shown that these substances can be indirectly oxidized at a boron-doped diamond electrode to small molecules (carboxylic acids and mineralized nitrogen-containing compounds). Abstract. Electrochemical oxidation at boron-doped diamond (BDD) electrodes was examined as a possible technique for the remediation of water contaminated with nitramine explosives. The advantage of BDD is that it promotes indirect oxidation by electrogenerated active intermediates, such as hydroxyl radicals. For the three explosives RDX, HMX, and CL-20, degradation in both acetonitrile/water mixtures and in water alone was suggested to involve an initial denitration, followed by spontaneous decomposition of the molecules, the net result being the complete transformation of the nitramines to small molecules. Although the rate of degradation increased with current density, the current efficiency was highest at low current densities.