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

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 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 pollutants oxidation (kobs ≈ 2 × 10-2 min-1 with initial benzoate concentration 50 μM) due to the buffer effect and the formation of Fenton-like active specie, CuCO3(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 is mainly decomposed into gaseous products, trace concentrations remain, exhibiting toxicity. Results with selective scavenger addition, electron paramagnetic resonance, NO(g) kinetics, and high resolution mass spectrometry suggested that the NH2OH not only acts as Cu(II) reducing agent (responsible for starting the Fenton reaction due to the in situ formation of H2O2 by Cu(I)/O2 reaction), it also changes the Fenton mechanism of Cu(I, II)/H2O2, suggesting that the formed reactive nitrogen species are the responsible for pollutant abatement rather than HO• or Cu(III).