Fenton-like oxidation–driven dual-mode detection of 2,4,6- trinitrophenyl-N-methylnitramine (tetryl) and 3-nitro-1,2,4-triazole-5-one (NTO) using single-step synthesized Cu2O@CuO nanocomposite

A novel detection approach based on single-step synthesized Cu2O@CuO nanocomposite (NC) assisted Fenton-like degradation followed by nitrite-mediated colorimetry has been evaluated for the selective separation and determination of 2,4,6-trinitrophenyl-N-methylnitramine (tetryl) and 3-nitro-12,4-triazole-5-one (NTO), which may accompany 2,4,6-trinitrotoluene (TNT) in explosive munitions. Mixed-valent nanocomposite: Cu2O@CuONC was successfully synthesized in an alkaline medium without adding a specific reducing agent. The bond cleavage releasing nitrite proceeds differently for the two analytes: •OH radicals, formed as a result of H2O2 decomposition catalyzed by Cu2O@CuONC, leads to the cleavage of the nitramine (N–NO2) bond through a non-selective attack on tetryl molecule leading to nitrite elimination, while for NTO molecule, radical species attach to the nitro-substituted C-3 carbon atom in the triazole ring, resulting in simultaneous nitrite elimination. The common major degradation product for tetryl and NTO, i.e. nitrite, reacts with sulfanilamide (SA) in acidic environment to form a diazonium salt, which then reacts with N-(1- naphthyl)ethylenediamine (NED) acting as a coupling agent to form a pink-colored azo dye. The final product could be monitored by both spectrophotometry and a smartphone application. The detection limits for tetryl and NTO were 25.0 µg L–1 and 2.0 µg L–1 (75.0 µg L–1 and 18.0 µg L–1 for smartphone application), respectively. The proposed method offers an innovative alternative to the traditional mechanism of forming Meisenheimer complexes for tetryl determination; it is also the first in literature to selectively detect tetryl and NTO, especially in explosive munitions containing TNT.