New Insights into the In Situ Fenton-like Process by Copper(II)-hydroxylamine Coupling: Reactive Species,...

This work studied the effect of pH, [O₂], H₂O₂ external addition, chelating agents, common anions, transition metals, and produced toxicity, in the process Cu-(II)/NH₂OH (employing benzoate as a probe). It was observed that (i) acidification by NH₂OH·HCl addition hindered the process significantly as the Cu-(NH₂OH)²⁺ is principally formed at pH = 6-8, (ii) high HCO₃ ^- concentrations (≥1 mM) accelerated the NH₂OH consumption (>95% in 5 min) and pollutant oxidation (k _obs ≈ 2 × 10^-2 min^-1 with initial benzoate concentration 50 μM) due to the buffer effect and the formation of a Fenton-like active species, CuCO_3(aq), (iii) the Mo-(VI)-peroxo species formed by Mo-(VI) reaction with the generated H₂O₂ consumed the NH₂OH, being a strong interference, and (iv) NH₂OH, although mainly decomposed into gaseous products, remained in trace concentrations, exhibiting toxicity. Results with selective scavenger addition, electron paramagnetic resonance, NO_(g) kinetics, and high resolution mass spectrometry suggested that NH₂OH not only acts as a Cu-(II) reducing agent (responsible for starting the Fenton reaction due to the in situ formation of H₂O₂ by Cu-(I)/O₂ reaction), but it also changes the Fenton mechanism of Cu-(I, II)/H₂O₂, suggesting that the formed reactive nitrogen species are responsible for pollutant abatement rather than HO^• or Cu-(III).