A novel self-assembled bimetallic zero-valent bismuth/iron (Bi/Fe-0) composite was synthesized, characterized, and used successfully to remove hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from wastewater. To assess the oxidative and reductive reactivities of Bi/Fe-0 nanoparticles (NPs), RDX degradation experiments were conducted in either ambient or anaerobic conditions, respectively. The best RDX degradation was achieved using 4%-Bi/Fe-0 (atomic ratio) NPs. In ambient conditions, concentrations of Fe2+ ions and H2O2 were lower in the Bi/Fe-0 solution than in the Fe-0 solution; this difference indicates that most Fe2+ ions and H2O2 reacted to produce hydroxyl radicals ((OH)-O-center dot) and superoxide radical anions (O-2(center dot-)), thereby resulting in the remarkable degradation of RDX. In anaerobic conditions, the presence of Bi increased the electron generation rate from the surfaces of the Bi/Fe-0 NPs. This increase was responsible for the excellent reductive degradation of RDX. Based on Density Functional Theory (DFT) calculations, the adsorption of water was endothermic on Fe-0 NPs and exothermic on Bi/Fe-0 NPs. Therefore, only the dissociation reactions of H2O in the Bi/Fe-0 system were spontaneous, and these reactions resulted in the prominent reactivity of the Bi/Fe-0 NPs. (C) 2014 Elsevier B.V. All rights reserved.