Role of H2O2 in the photo-transformation of phenol in artificial and natural seawater.
In previous works, it was observed that phenol photo-induced transformation in natural seawater (NSW) mediated by natural photosensitizers occurs and leads to the formation of numerous hydroxylated, condensed, halogenated and nitroderivatives. Irradiation of NSW added with phenol and iron species had provided the enhanced formation of several halophenols, suggesting a central role played by iron species on the phenol halogenation in marine water. In this paper, we focus on hydrogen peroxide, another key photosensitizer, and its interaction with iron species. The ability of Fe(II)/Fe(III) and H(2)O(2) species to act as photo-sensitizers towards the transformation of organic compounds in seawater was investigated under simulated solar radiation. Light activation is necessary to induce the transformation of phenol, as no degradation occurs in the dark when either H(2)O(2) or iron/H(2)O(2) are initially added to artificial seawater (ASW). Fe(II) is easily transformed into Fe(III), assessing that a Fenton reaction (dark, Fe(II)/H(2)O(2)) does not take place in marine environment, in favour of a photo-activated reaction involving Fe(III) and H(2)O(2). When NSW is spiked with H(2)O(2) and Fe(III), halophenols' and nitrophenols' concentration decreases and completely disappears at high hydrogen peroxide concentration. Since Fe(II) and Fe(III) in spiked seawater induce an enhanced formation of haloderivatives, an excess of hydrogen peroxide act as scavenger towards the photo-produced chloro/bromo radicals, so hindering halogenation process in seawater. Hence, even if hydrogen peroxide efficiently induces the ·OH radical formation, and could then promote the phenol phototransformation, nevertheless it is negligibly involved in the production of the intermediates formed during phenol photolysis in seawater, whose formation is necessarily linked to other photosensitizer species.
Dipartimento di Chimica, Università di Torino, via P. Giuria 5, 10125 Torino, Italy. paola.calza@unito.it
Paola
P
Calza
Laura
L
Campra
Ezio
E
Pelizzetti
Claudio
C
Minero