Standard potential hydroxyl radical

The energy band diagram for Ti02 in pH 7 solution is shown in Fig. 2.7. As shown, the redox potential for photogenerated holes is +2.53 V vs. the standard hydrogen electrode (SHE). After reaction with water, these holes can produce hydroxyl radicals ( OH), whose redox potential is only slightly decreased. Both are more positive than that for ozone. The redox potential for conduction band... 

Like that of the hydrated electron and the hydrogen atom, the potential of the hydroxyl radical has long been the subject of estimates based on thermochemical cycles involving the free energy of hydration of OH the results of these calculations appear, for example, in Standard Potentials (pp. 59-64). Recently, however, there have been two direct determinations of E° for the OH/OH- couple. In the first, Schwarz and Dodson (279) used pulse radiolysis to measure the equilibrium constants for... 

These equations refer to one-electron reductions versus the standard hydrogen electrode. Substrates M with more positive reduction potentials for the couple M/ M are stronger oxidants than substrates with lower or negative E. Therefore, in this case, M is easier to reduce. Eor example, the couple Cl /Cr has a reduction potential E of 2.200 to 2.600 V, and therefore chloride ions can theoretically be oxidized in water to chlorine atoms by hydroxyl radicals with E( OH, H / H20) = 2.730 V, according to Eq. 6-3 ... 

The hydroxyl radical is a powerful oxidant with a standard reduction potential of 2.73 V in acidic solution. In neutral solution where the free energy of neutralization of OH by the proton is not available, the reduction potential is calculated to be 1.9 V (Table 2). 

It is perhaps helpful at this stage to look at the reactions which free iron ions catalyze. This is chemistry which was originally developed by Fenton in 1894 in order to improve the oxidizing power of hydrogen peroxide by the production of hydroxyl radicals, OH , which have a standard electrode potential of 2.8 V which is more positive than those of ozone, hydrogen peroxide itself (1.8 V) potassium permanganate and chlorine and only marginally less than the standard reduc-... 

Of these products it is the three radical species which are the most reactive. The solvated electron and hydrogen atom have reduction potentials (Eo) of —2.87 and —2.30 V versus the standard hydrogen electrode (SHE), respectively [22], and hence they are extremely reactive reductants. The hydroxyl radical is a highly oxidising species with a reduction potential (Eo) of 2.65 V vs SHE [22]. 

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