Effective adsorptive removal of 2,4,6-trinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine by pseudographitic carbon: kinetics, equilibrium and thermodynamics

Abstract

Environmental contextExplosive organic compounds such as 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are major constituents of ammunition materials. These compounds are of environmental concern because they can have a significant impact on ecosystems and humans. Through investigations of adsorption kinetics, isotherms and thermodynamics, we demonstrate the suitability of pseudographitic carbon for removing TNT and RDX from groundwater, and additionally confirm the viability of the use of pseudographitic carbon through comparison with other adsorbents. Abstract2,4,6-Trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) – common explosives in military munitions – can easily enter groundwater supplies and have an adverse impact on human health. There is great concern about the need to remove these explosives from groundwater, and this study presents pseudographitic carbon (PGC) prepared from edible sugar as a material to remove explosives from contaminated groundwater via adsorption. The purity and physicochemical characteristics of the PGC were characterised using advanced spectroscopic techniques. The adsorption mechanism and its efficiency were investigated in terms of the non-linear adsorption kinetics, isotherms and thermodynamics using TNT and RDX adsorption data. The results of the non-linear modelling indicate that TNT and RDX adsorption was determined by rate-limiting monolayer exothermic adsorption on the homogeneous PGC surface. Ionic strength was studied with various ions, and the results indicate that the adsorption of TNT and RDX was significantly influenced by divalent cations and the carbonate anion. The results of desorption and re-use tests indicate that acetone and acetonitrile are the best desorbing agents. The PGC can be recycled and re-used for up to 3 cycles, with insignificant loss in adsorption efficiency. Finally, the PGC was applied to real spiked groundwater to evaluate its applicability in the field in removing TNT and RDX. The overall results indicate that PGC is a cost-effective and efficient adsorbent that effectively removes the organic explosives from groundwater, thereby reducing risk to humans and the aqueous environment.