New insights into the degradation mechanism of TNT in supercritical water: Combining density functional theory with the reactive force field

Supercritical water (SCW) has been proven to be an efficient method for the degradation of TNT explosive wastewater, resulting in a reduction of environmental pollution. To investigate the decomposition mechanism of TNT under various SCW conditions, specific ReaxFF parameters for TNT and H2O were utilized. The findings indicate that the SCW gasification process generates the toxic compound HCN, which can be rapidly oxidized by introducing O2. The stable small molecule products are CO2, CO, H2O, N2, etc. The higher pressures effectively curtail the initial production of CO and facilitate the conversion of CO into CO2. The addition of O2 significantly enhances the complete degradation of TNT, particularly increasing the yield of CO2. The density functional theory was used to investigate the intricate formation pathway from TNT to azepine, which was assumed to speed up the decomposition of TNT. The development of azepine was then caused by a rearrangement from C-N (OH)O to C(O)-NOH and NO rearrangement. The activation energy of the decomposition of TNT in SCW was 85.1 kJ/mol, which is much smaller than the activation energy of thermal decomposition (140 kJ/mol), demonstrating the superiority of the decomposition of TNT in SCW.