Ozone redox potential

Ozone is very much more reactive than oxygen and is a powerful oxidising agent especially in acid solution (the redox potential varies with conditions but can be as high as + 2.0 V). Some examples are 1. the conversion of black lead(ll) sulphide to white lead(II) sulphate (an example of oxidation by addition of oxygen) ... 

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... 

Hazardous waste could be successfully and mostly cheaply eliminated with those methods. Strong oxidizing materials (chlorine) could be applied when dealing with soluble matter. Ozone could be also used as oxidizing agent. Ozone has higher redox potential than chlorine so the oxidizing state in reactions could be much easier reached [ 1 ]. 

Only fluorine, atomic oxygen and FgO have higher redox potentials. The gas oxidises moist sulphur to jH2S04, raises silver(I) compounds to the 2 state and converts olefinic compounds to ozonides. The reaction 2O3 -> SOg, which is catalysed by many metals and metal oxides, is exothermic and rapid above 200°. Gaseous ozone is deeper blue than oxygen it condenses at — 112° to a dark blue liquid which freezes at —193° to a dark purple solid. Surprisingly, the liquid is not completely miscible with liquid oxygen. 

The use of ozone os on oxidant for industrial wastes containing cyanides and other reducible toxic substances appears worthy of careful investigation. The oxidation of simple cyanides by ozone is rapid and complete. Mass transfer controls the absorption. The use of packed towers or sieve plate towers is indicated, and the maintenance of a pH of at least 9.0 is recommended. The destruction of cyanates and cyanide complexes is slower than the cyanide oxidation. These substances are destroyed if sufficient contact time and proper pH control are maintained so that these slower reactions can take place. The use of redox potential to control the degree of oxidation appears promising. Proper interpretation of the redox potential of the treated waste will give an excellent indication of the effectiveness of the treatment and the degree of removal of cyanide and cyanate. 

The solution of cyanide ion contains no ozone in solution during this cyanide phase, as may be determined by the oxidation potential of the solution. The redox potential will remain at a low value, rising slowly and gradually as the cyanide is consumed (Figure 2). When the cyanide ion practically has all been oxidized, an immediate and sudden rise in potential is experienced, at which point the solution is an oxidizing one and releases iodine from potassium iodide solutions. 

Figure 7. Effects of ozone on redox potential of solutions of cyanate ion...

Then 0.01 mole of potassium cyanate was dissolved in a small amount of water and added to a saturated solution of ozone in 3100 ml. of neutral distilled water, which was agitated thoroughly. The redox potential fell to a minimum point, rose slightly, and then fell off in a normal decay curve. The raising of the pH which would follow upon addition of cyanate could catalyze the decomposition of ozone, but would not account for the minimum in the curve. Cyanate solutions will, therefore, exercise an ozone demand, whether through hydrolysis or oxidation, and ozone will be consumed until the demand is satisfied. 

Figure 8 shows the effect of ozone on the redox potential of ferrocyanide solutions. Successive additions of ozone show a decreased ozone demand in the solution. 

Figure 9. Effect of agitation on decay of redox potential of ozonated cyanate solutions...

Figure 10. Decay of redox potential of saturated calomel electrode-platinum electrodes in agitation of ozonized distilled water at 25° C.

To obtain additional information about ozone activity at the concentrations of greatest biological interest, oxidation-reduction potentials of buffered bacterial suspensions were determined after addition of various amounts of ozone. It was reasoned that the oxidation-reduction potential at or close to the lethal concentration would exhibit a demonstrable change indicative of the corresponding activity. Figure 2 presents the results of the experiment there is a sharp break in the redox potential at an ozone concentration comparable to the level found to represent the lethal dose in the dosage-contact time experiments. A differential plot of the same data emphasizes this information (Figure 3). 

For an enzyme to be suitable for the metabolism of ozone, its copper-binding site would have to catalyze redox reactions at very high redox potentials. The redox couple Cu(II)/Cu(III) seems to be suitable for this purpose. The stabilization of Cu(III) requires hard ligands, such as tyrosines, hydroxyl anions, phos-... 

This value for the redox potential shows clearly that ozone is one of the... 

Redox potentials for many elements are known to be pH dependent and electrochemical or ozone oxidation of Pr " and Tb in alkaline conditions has been reported to give tetravalent species in the presence of carbonate ions. Presumably, these Ln species are carbonate complexes. Other complexes of Tb have been reported with tellurate and periodate (both of which would be oxidation-resistant ligands) in both solution and soUd state. ... 

The standard redox potential E° of peroxodisulfate in aqueous solution is 2.01 V, which is comparable to those of other AOP oxidants ozone (,E°— 2.07 V) and hydrogen peroxide E°- 1.78 V). Peroxodisulfate is not an active oxidant at ambient temperature, but it is activated with UV radiation or heating. 

Using another oxidant with a higher redox potential as compared with chromium anhydride (e.g., potassium permanganate) during the purification in a liquid medium, or a strong oxidant dnring the gas-phase pnrification (e.g., ozone)... 

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