Degradation kinetics of hydroxy and hydroxynitro derivatives of benzoic acid by fenton-like and photo-fenton techniques: A comparative study

DANIELA NICHELA; MÉNANA HADDOU; FLORENCE BENOIT-MARQUIÉ; MARIE-THÉRÈSE MAURETTE; ESTHER OLIVEROS; FERNANDO S. GARCÍA EINSCHLAG

APPLIED CATALYSIS B-ENVIRONMENTAL

ELSEVIER SCIENCE BV

Año: 2010 vol. 98 p. 171 - 179

0926-3373

The oxidative degradation of a series of hydroxy and hydroxynitro derivatives of benzoic acid byFenton-like and photo-Fenton processes was compared under identical conditions (initial concentrations,pH and temperature). In spite of closely related chemical structures, (2-hydroxybenzoic (2HBA),2,4-dihydroxybenzoic (24DH-BA), 2-hydroxy-5-nitrobenzoic (2H5N-BA), 4-hydroxy-3-nitrobenzoic(4H3N-BA) and 2-hydroxy-4-nitrobenzoic (2H4N-BA) acids), the degradation timescales were remarkablydifferent. A common feature was, however, that autocatalytic decay profiles were displayed by thesubstrates and H2O2. A simple equation, which may be used as a valuable tool for a semiquantitativeanalysis of the main kinetic features of the inverted “S” profiles, is presented. In addition, a method forthe estimation of the relative contribution of photoinduced pathways in photo-Fenton systems (photoenhancementfactors) is proposed.In order to assess the key processes governing the kinetic profiles observed, complementary studieswere performed to evaluate the formation of ferric complexes, the reactivity towards HO• and Fe(II) productionefficiencies. Except for 4H3N-BA, the model substrates form highly stable complexes with Fe(III).Competition experiments showed that the reactivities of both the substrates and the ferric complexeswith hydroxyl radicals cannot explain the large timescale differences observed in Fenton-like and photo-Fenton systems. The comparison of Fe(II) production under irradiation in the absence of H2O2 with thedecay profiles observed in both Fenton-like and photo-Fenton systems confirms that the main factor controllingthe autocatalytic behavior is the formation of organic intermediates that are capable of reducingFe(III) species. An additional factor in the photo-Fenton process may be the efficiency of photoinducedFe(II) production, which is affected by complex formation since the studied complexes exhibit a lowerefficiency of Fe(III) photoreduction than the Fe(III)–aquo complex.