Graphene-based Adsorption and Stabilization for Environmental Treatment of Insensitive Munitions Compounds

Abstract

Insensitive munitions (IM) formulations are being pursed as potential safer alternatives to traditional formulations, and strategies to enhance their environmental sustainability are being considered. Thus, graphene nanoplatelets (GnPs) were evaluated for environmental management applications for IM compounds 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), nitroguanidine (NQ), and methylnitroguanidine (MeNQ) in addition to legacy munitions compounds (MCs) 2,4,6-trinitrotoluene and hexahydro-1,3,5-trinitro-s-triazine (RDX). Specifically, immobilization capabilities regarding adsorption and solidification-stabilization (S-S) were investigated. Evaluations were conducted with individual MCs to determine performance and underlying mechanisms of environmental management strategies. Adsorption studies were conducted with each MC to inform isotherms and kinetics in comparison against benchmark granular activated carbon (GAC). Evaluations of various solution conditions; including pH, ionic strength, and temperature; were conducted to determine influences on performance. Following adsorption, samples of GnPs with each adsorbed MC were exposed to high-pH and comparative solutions to determine capabilities related to release of MCs and regeneration and reuse of GnPs. S-S studies were conducted to assess leaching capabilities of DNAN, NTO, and RDX from cement pastes prepared with and without GnPs. Adsorption evaluations demonstrated that GnPs more rapidly adsorbed each MC and that π-π interactions promote greater adsorption capacities of DNAN and TNT relative to GAC. Solution pH and ionic strength impacted NTO adsorption, and high-pH solutions promoted its desorption via electrostatic repulsion. Furthermore, high pH caused alkaline hydrolysis of the other MCs on the surface of GnPs, supporting regeneration of the adsorbent. S-S evaluations demonstrated that dose-dependent release of NTO and a DNAN breakdown product related to alkaline hydrolysis. NTO adsorbed to the cementitious matrices but was released as cement pastes degraded at low pH. Conversely, equivalent DNAN was released from crushed cement pastes exposed to reagent water but appeared to be adsorbed as cement degraded. Furthermore, GnPs limited release of equivalent DNAN, and none was observed in leachates from monolithic samples. RDX fully degraded via alkaline hydrolysis within cement pastes and was not observed in evaluated leachates. Overall, this research suggests the promising capabilities of graphene-based materials for environmental management strategies regarding insensitive and legacy MCs.