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

## TL;DR

This study explores how copper and hydroxylamine interact in a chemical process, revealing new insights into how pollutants can be broken down.

## Contribution

The study reveals a new mechanism where hydroxylamine changes the Fenton process involving copper, leading to reactive nitrogen species instead of hydroxyl radicals.

## Key findings

- High bicarbonate concentrations accelerate hydroxylamine consumption and pollutant oxidation via a Fenton-like active species.
- Hydroxylamine acts as a copper(II) reducing agent and alters the Fenton mechanism to produce reactive nitrogen species.
- Molybdenum(VI) interferes by forming a peroxo species that consumes hydroxylamine.

## Abstract

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, 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 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).