Nitrobenzene degradation in Fenton-like systems using Cu(II) as catalyst. Comparison between Cu(II)- and Fe(III)-based systems

Paraquat removal from water by oxidation with Fenton's reagent

Effects of Fenton reagents, iron and hydrogen peroxide, on the generation of hydroxyl radicals ( OH) during photo-Fenton degradation of acetaldehyde dissolved in water were examined. The dynamic change in OH radical concentration during the acetaldehyde degradation by the photo-Fenton process was measured using a coumarin fluorescence probing technique. The OH radical concentrations increased with increasing initial Fe concentrations within the Fe dosage range examined in this study. With increasing acetaldehyde loading the OH radical concentration decreased. The OH radical concentration changed rather complicatedly as the acetaldehyde degradation by the photo-Fenton oxidation process proceeded. The dynamic change in OH radical concentration could be divided into four phases: the OH radical concentration instantaneously and significantly increased just after the start of photo-Fenton oxidation process (Phase I), subsequently decreased (Phase II), increased again after reaching its minimum value (Phase III), and gradually decreased after the OH radical concentration reached a maximum point (Phase IV). This complicated change in OH radical concentration during photo-Fenton degradation of acetaldehyde could be rationally described by the Fe-redox cycle via the Fe–organic complex formation and its oxidation by dissolved oxygen besides the Fenton and photo-Fenton reactions. It was found that the oxidation of iron–organic complexes formed by ferric iron with acetaldehyde and its degradation products accelerated the rate of Fe-redox cycle. On the other hand, the formation of Fe–organic complexes led the decrease in Fe ions available for the Fenton and photo-Fenton reactions.

Iron redox cycling in hydroxyl radical generation during the photo-Fenton oxidative degradation: Dynamic change of hydroxyl radical concentration

Submicron sized water-stable metal organic framework (bio-MOF-11) for catalytic degradation of pharmaceuticals and personal care products.

Paracetamol degradation intermediates and toxicity during photo-Fenton treatment using different iron species

The oxidative degradation of a series of hydroxy and hydroxynitro derivatives of benzoic acid by Fenton-like and photo-Fenton processes was compared under identical conditions (initial concentrations, pH and temperature). In spite of closely related chemical structures, (2-hydroxybenzoic (2H-BA), 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 remarkably different. A common feature was, however, that autocatalytic decay profiles were displayed by the substrates and H 2 O 2 . A simple equation, which may be used as a valuable tool for a semiquantitative analysis of the main kinetic features of the inverted “S” profiles, is presented. In addition, a method for the estimation of the relative contribution of photoinduced pathways in photo-Fenton systems (photoenhancement factors) is proposed. In order to assess the key processes governing the kinetic profiles observed, complementary studies were performed to evaluate the formation of ferric complexes, the reactivity towards HO and Fe(II) production efficiencies. 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 complexes with 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 H 2 O 2 with the decay profiles observed in both Fenton-like and photo-Fenton systems confirms that the main factor controlling the autocatalytic behavior is the formation of organic intermediates that are capable of reducing Fe(III) species. An additional factor in the photo-Fenton process may be the efficiency of photoinduced Fe(II) production, which is affected by complex formation since the studied complexes exhibit a lower efficiency of Fe(III) photoreduction than the Fe(III)–aquo complex.

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

In the context of our work on the oxidative degradation of a series of hydroxyl derivatives of benzoic acid (HBAs) by Fenton-like and photo-Fenton processes, we present a comprehensive study of the factors that affect the reduction of Fe(III) species, the rate limiting step in the Fenton reaction. We have investigated: (i) the formation of Fe(III)–HBA complexes, (ii) the ability of these complexes to participate in reductive pathways, and (iii) the formation of intermediate products capable of reducing ferric species. The results show that salicylate-like HBAs form stable bidentate ferric complexes in aqueous solutions at pH 3.0 and that Fe(III) complexation significantly decreases the overall degradation rates in Fenton systems by slowing down Fe(II) production through both dark and photo-initiated pathways. Interestingly, in contrast to ferric complexes of aliphatic carboxylates that undergo a photo-induced decarboxylation upon excitation in the 300–400 nm wavelength range, ferric–salicylate complexes yield Fe(II) and hydroxyl radicals by oxidation of water molecules in the coordination sphere of the metal center. However, their efficiencies are significantly lower than that of the Fe(III) aqua complex. Moreover, Fe(III)–HBA complexes are inert upon excitation of the LMCT bands involving the organic ligand (i.e., 400–600 nm). As observed for other aromatic compounds, Fe(III)-reducing intermediates formed during the Fenton oxidation of HBAs play a key role in iron cycling. The analysis of the primary oxidation/hydroxylation products as well as Fe(III)-reduction studies showed that, among dihydroxy aromatic derivatives, hydroquinone-like structures were much more efficient than catechol-like structures for reducing Fe(III). Although all trihydroxy derivatives produced Fe(II), ring opening reactions prevailed under the conditions of the Fenton reaction. The results of our investigation on the Fenton oxidation of HBA derivatives show that, in each particular case, the complex interplay of the aforementioned factors should be carefully evaluated for developing optimal applications of Fenton processes at a technological level.

Iron cycling during the autocatalytic decomposition of benzoic acid derivatives by Fenton-like and photo-Fenton techniques

The kinetics and mechanisms of the oxidative degradation of 2,4-dihydroxybenzoic acid (2,4-DHBA) by the Fenton and photo-Fenton processes were investigated in detail by a combination of HPLC, IC, and TOC analyses. The formation of 2,3,4-trihydroxybenzoic acid (2,3,4-THBA) at an early oxidation stage shows that hydroxylation of the aromatic ring is the first step of the process. This intermediate was able to reduce FeIII and to contribute to the recycling of FeII. Complete mineralization could only be achieved under irradiation (photo-Fenton). A detailed study of the dependence of the rate of mineralization on the concentration of H2O2 and dissolved O2 was carried out. It was found that, even at a low initial concentration of H2O2, mineralization by the photo-Fenton process was complete in a relatively short time, provided that the O2 concentration was high enough, indicating that O2 may, at least in part, substitute H2O2. Channeling reaction pathways toward O2 rather than H2O2 consumption is of particular interest for the technical development of the photo-Fenton process.

Oxidative Degradation of 2,4-Dihydroxybenzoic Acid by the Fenton and Photo-Fenton Processes: Kinetics, Mechanisms, and Evidence for the Substitution of H2O2 by O2

Abstract We have investigated the efficiency of the coupling of adsorption on a zeolite material (DAY) and UV or V-UV irradiation for the treatment of VOC containing air streams. We have compared the efficiency of photodegradation of two pollutants (1-butanol and toluene) in the absence and in the presence of TiO2 deposited on DAY (DAY/TiO2). Irradiation was performed with two different excimer lamps emitting in the V-UV at 172 nm and in the UV at 308 nm. The gaseous effluent was analyzed on-line at the exit of the photochemical reactor by GC and FTIR. The adsorbents (DAY and DAY/TiO2) were analyzed before and after irradiation by solid state NMR, and the residual organic products remaining on the solids by GC-MS after extraction. The results show that the coupling of adsorption on DAY/TiO2 and V-UVirradiation is highly efficient both for VOC mineralization and adsorbent regeneration. This efficiency results from the synergy between the important contribution of VUV photolysis to the oxidative degradation of the VOC and the photocatalytic effect of TiO2 under V-UV irradiation at the DAY/TiO2 surface, preventing adsorbent fouling as observed in the absence of TiO2. The contribution of TiO2 was particularly remarkable in the case of toluene.

Coupling of Adsorption on Zeolite and V-UV Irradiation for the Treatment of VOC Containing Air Streams: Effect of TiO2 on the VOC Degradation Efficiency

Ménana Haddou

Papers

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

Iron cycling during the autocatalytic decomposition of benzoic acid derivatives by Fenton-like and photo-Fenton techniques

Oxidative Degradation of 2,4-Dihydroxybenzoic Acid by the Fenton and Photo-Fenton Processes: Kinetics, Mechanisms, and Evidence for the Substitution of H2O2 by O2

Coupling of Adsorption on Zeolite and V-UV Irradiation for the Treatment of VOC Containing Air Streams: Effect of TiO2 on the VOC Degradation Efficiency