Fenton chemistry

Although the activation of hydrogen peroxide by reduced transition metals has been known for almost 100 years as Fenton chemistry,  

For the Fenton process to occur the L2Fe II-OH bond must have a -AGbf value of at least 51 kcal [for (I l2O) Fe -OH (aqueous, pH 2 E , -F 0.4 V versus NHE) the value is 54 kcal see Chapter 3]. At pH 0 the potential for the Feni/n(H2O)63 /2+ redox couple (E°, -t- 0.77 V versus NHE) indicates that the (H2O)5 FeFI-OH2 bond has a -AGbf value of 45 kcal, which is consistent with 

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Fenton chemistry is dependent on the formation of free radicals. 

A Catalytic Oxidation Tool. Fenton Chemistry in Solid Catalyst Synthesis 127... 

Fenton chemistry comprises reactions of H2O2 in the presence of iron species to generate reactive species such as the hydroxyl radical OH. These radicals ( = 2.73 V) lead to a more eflident oxidation chemistry than H2O2 itself (E° = 1.80 V). 

Although Fenton chemistry has been solely researched in water and soil purification, it can also be an added-value tool for catalyst preparation. The next sections review this concept including the following ... 

We discuss here a combined process including detemplation and Fe incorporation by ion-exchange in the zeolite framework [147]. To achieve this, oxidants to decompose the organic template and Fe-cations for exchange are needed. Both requirements are in harmony with Fenton chemistry. The OH radicals can oxidize the template and the Fe-cations be exchanged simultaneously. 

Recent reports describe more sophisticated detemplation methods. However, they are limited to mesoporous materials for the reasons described before. We show how Fenton chemistry can fulfill various missing challenges (i) it provides a powerful oxidation capacity at low(er) temperatures and (ii) it can work for microporous compounds as well. 

Pradhan AA, Gogate PR (2009) Degradation of p-nitrophenol Using Acoustic Cavitation and Fenton Chemistry. J Haz Mat 173 517-522... 

Iron or copper complexes will catalyse Fenton chemistry only if two conditions are met simultaneously, namely that the ferric complex can be reduced and that the ferrous complex has an oxidation potential such that it can transfer an electron to H2O2. However, we must also add that this reasoning supposes that we are under standard conditions and at equilibrium, which is rarely the case for biological systems. A simple example will illustrate the problem whereas under standard conditions reaction (2) has a redox potential of —330 mV (at an O2 concentration of 1 atmosphere), in vivo with [O2] = 3.5 x 10 5 M and [O2 ] = 10 11 M the redox potential is +230 mV (Pierre and Fontecave, 1999). 

The fact that reaction (12) is much slower than reaction (8), implies that Fe is faster depleted from the solution. As a result, Fenton process is halted because the redox chain cannot be supported itself. In addition, it is accepted that (Pignatello 1992 Boye et al. 2003) the hydroperoxyl radical (HO2 ) has a much lower oxidant power than OH. In the presence of organics, Fenton chemistry is even more complex because hydroxyl radical, both iron cations and the oxidation products enter into a series of consecutive and parallel reactions. An example of the complexity of these reactions is discussed elsewhere (Gozzo 2001) but a brief description is given here. The initial step for an organic substrate (R-H) oxidation starts with the interaction of itself with OH, according to (Walling and Kato 1971) ... 

A detailed kinetie study in the Fenton chemistry, based on spectrophotometric measurements of evolved O2 and the disappearance of Fe, has shown the existence of a new intermediate Kremer 1999). It was identified as the mixed valence binuclear species... 

However, experimental evidenee points towards another feasible interpretation the couple Fe /Fe regeneration, during the Fenton chemistry is not effieient due to chemical speciation. Indeed, the effieieney of the Fenton chemistry can be enhaneed (Pignatello 1992 Huston and Pignatello 1999) by UV light irradiation (X 300 nm) because the photoreduction of Fe (from equation 8) and H2O2 aetivation are another source of OH radicals and Fe ... 

A similar situation was observed (Kremer 2003) during the homogeneous catalytic activation of H2O2 in the presence of Fe Fe ions disappear from the bulk solution at the initial stage of the Fenton chemistry and they are not regenerated to maintain the redox chain. 

The aim of this section is to support the hypotheses that chemical speciation of iron ions is one of the main drawbacks in the performance of Fenton chemistry during the organic... 

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