Novel self-assembled bimetallic structure of Bi/Fe(0): the oxidative and reductive degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX).

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 Fe(2+) ions and H2O2 were lower in the Bi/Fe(0) solution than in the Fe(0) solution; this difference indicates that most Fe(2+) ions and H2O2 reacted to produce hydroxyl radicals (OH) and superoxide radical anions (O2(-)), 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.