Page 197 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

182 Principles and Methods

2 1 2.
.FesIIIdSO 3 1 h vb m .FesIIId 1 SO 3 (51)
2. 2.
2
SO 3 1 O h SO 5 (52)
2. 22 22 2.
SO 5 1 SO 3 h SO 4 1 SO 4 (53)
2. 22 22 2.
SO 5 1 SO 3 h SO 5 1 SO 3 (54)
2. 22 22 2.
SO 4 1 SO 3 h SO 4 1 SO 3 (55)
22 22 22
SO 5 1 SO 3 h 2SO 4 (56)

2.06 eV;
The other iron(III) oxide polymorphs (e.g., -FeOOH, E g
-FeOOH, E 2.12 eV; -FeOOH, E 2.10 eV; -FeOOH, E
g
g
g
1.94 eV; -Fe O E 2.03 eV) are photocatalytic for certain reactions
2
g
3,
[42]. In general, the observed order of relative photochemical reactivity
toward SO oxidation [43] is -FeOOH -Fe O -Fe O -FeOOH
2
2
3
3
2
-FeOOH -FeOOH, while in the case of C O 2 oxidation [44–46]
2
4
the relative catalytic order is ferrihydrite (am-Fe(OH) ), -Fe O 3
3
2
-FeOOH -Fe O -FeOOH -FeOOH.
3
2
2
e >h 1 2 1
2 . FeOH 1 hv h . FesIIdOH 1. FesIVdOH (57)
2 1
e tr h tr
1 22 2.
.FesIVdOH 1 C 2 O 4 h .FesIIIdOH 1 CO 2 1 CO 2 (58)
2 2.
.FesIIdOH 1 O 2 h .FesIIIdOH 1 O 2 (59)
Similar reactions occur with other carboxylic and dicarboxylic acids
on the surface of the iron oxides and oxyhydroxides leading to superoxide
and hydrogen peroxide formation. Pehkonen et al. [46] found that the
O formation on a series of iron oxide polymorphs depended
rates of H 2 2
on the chemical nature of the carboxylate electron donor where HCO 2

CH 3 CO 2 CH 3 CH 2 CH 2 CO 2 .
Metal Sulfide Surface Chemistry and
Free Radical Generation
Metal sulfide and related chalocogenide semiconductors are used in a
variety of electronic applications. For example, CdS, which is an n-type
semiconductor with E g 2.4 eV, has been shown to have photocatalytic
activity for H 2 production under visible light irradiation under anoxic con-

ditions in water in the presence of electron donors such as C 2 H 5 OH, HS
2
and SO 3 .