Photolysis by UVA-visible light and thermal degradation of TNT in aqueous solutions according to aerodynamic thermal breakup droplet ionization mass spectrometry

Abstract

The mechanism of photolytic degradation of 2-4-6-trinitrotoluene (TNT) in an aqueous solution (initial concentration 102 mg L−1) by UVA-visible light (>320 nm) was investigated by aerodynamic thermal breakup droplet ionization mass spectrometry. For photolysis, a DRK-120 mercury-quartz lamp was used. The final and intermediate products of the photolysis reaction were compared with known products of TNT transformation in the environment. The first step in the photolysis process under our conditions was found to be the association of TNT molecules into a fairly stable dimer. The TNT dimer formation proceed through the formation of a Meisenheimer complex. Thermal degradation of the TNT dimer in microdroplets within a heated capillary used as a flow reactor was studied next. It was shown that the degradation of the TNT dimer in microdroplets occurs very quickly (2.1 ms) at heating (up to 200–250 °C). Of course, heating an aqueous aerosol requires energy, but the transformation of TNT can be controlled using a combination of photo- and thermal treatments. We hope that these results will help to reduce the toxicity of TNT contaminants and remove nitroaromatic compounds from water at ambient conditions. In this work, the TNT dimer formed at the first stage is transformed with the loss of NO2 fragments or water. In addition, further polymerization of TNT is observed.