Alkaline hydrolysis for degrading the emerging munitions contaminant methylnitroguanidine and regenerating graphene nanoplatelets for sustainable adsorption of munition compounds

Abstract

Alkaline hydrolysis has proven to be an effective treatment technique for several emerging and legacy munition compounds (MCs), including 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-s-triazine (RDX), 2,4-dinitroanisole (DNAN), and nitroguanidine (NQ). Building on this success, this study evaluates its effectiveness in degrading the emerging insensitive MC methylnitroguanidine (MeNQ) in comparison to NQ. Additionally, the feasibility of regenerating graphene nanoplatelets (GnPs) following adsorption of MCs, including MeNQ, NQ, NTO, TNT, DNAN, and RDX, is investigated. This study is among the first to successfully evaluate MeNQ treatment and proposes a novel strategy to regenerate GnPs for further environmental remediation. Regeneration performance in high-pH solutions was compared with processes using a 30:70 solution of acetonitrile:water and reagent water alone to further determine pH- and solvent-based interactions. In high-pH solutions, NTO was desorbed via electrostatic repulsion, while the other MCs degraded, generating breakdown products consistent with both previous studies and current findings. Additionally, the aqueous ammonium produced during degradation may have been removed by GnPs. The organic-aqueous blend enhanced MC removal, with recovery largely correlating with aqueous solubility, though π-π interactions may have hindered desorption. Adsorption following desorption with these techniques resulted in higher capacities compared to systems using reagent water alone, where desorption aligned with adsorption isotherms. Overall, this study provides valuable insights into MeNQ treatment and the reuse of GnPs for sustainable water remediation.