The current study investigates the fate of sorbed nitroaromatics on the surface of pyrogenic carbonaceous matter (PCM) to assess the feasibility of a PCM-promoted hydrolysis. The degradation of two nitroaromatic compounds, 2,4,6-trinitrotoluene (TNT) and 2,4-dinitroanisole (DNAN), was observed at pH 7 in the presence of graphite powder, a model PCM. By contrast, no decay occurred without graphite. Reactions followed first-order decay, with rate constants of 0.258 ± 0.010 d-1 and 0.034 ± 0.001 d-1 for TNT and DNAN, respectively. Further studies were carried out using TNT as a model compound. TNT decay demonstrated strong pH dependence, with no reaction at pH 3-5 but rapid degradation at pH 6-10. Moreover, TNT decay at different pH conditions along with sorption kinetics at pH 3 were fitted with the Langmuir Kinetic Model. Results suggest that base-catalyzed hydrolysis was important in the observed TNT decay. The activation energy (Ea) for TNT decay was obtained by measuring reaction rate constants at different temperatures with or without graphite. No significant difference was observed in the obtained Ea values. However, the addition of tetramethylammonium cation ((CH3)4N+) was able to promote TNT decay possibly due to their ability to attract OH- from the aqueous solution, leading to an increase in the sorbed OH- concentrations. Nitrite and a Meisenheimer complex were identified as degradation products for TNT. Other PCM, such as biochar, also demonstrated a comparable ability in promoting TNT decay at pH 7. Furthermore, TNT decay was investigated in soil samples with or without biochar amendments (4% w) at pH 7. A rapid degradation of TNT was observed with biochar, corresponding to a calculated half-life of 3.12 ± 0.21 days, while no TNT decay occurred in controls without biochar. Our results suggest that PCM can facilitate TNT and DNAN decay via a surface-promoted hydrolysis, indicating potential for in situ soil remediation technologies.

Surface-promoted hydrolysis of 2,4,6-trinitrotoluene and 2,4-dinitroanisole on pyrogenic carbonaceous matter

255th National Meeting (2018)

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