conversion into OHradicals (e.g.,Eqs. 34 and 37). The yield and
convenience of the solar photocatalytic degradation can be
enhanced by Fe(III) species coupled with TiO 2
(145,158,159,226– 229 ).

B. COPPERCOMPLEXES

Other potential transition metal photocatalysts occur in water
basins in much lower concentrations and thus the effect of their
photoreactivity is decidedly smaller. Among them only the copper
contribution was more extensively studied. In soils most of the
metal is in an insoluble form or bound to various inorganic and
organic ligands. Only in storm water and subsequently urban
rivers, the copper concentration frequently exceeds the freshwater
quality criteria. Generally, the main inorganic cupric species pres-
ent in freshwater systems are Cu^2 þ, Cu(OH)þ, Cu(OH) 2 , and [Cu
(CO 3 ) 2 ]^2
, and these make up 98% of the dissolved inorganic cop-
per; the rest 2% of dissolved inorganic copper is coordinated mostly
by chlorides and phosphates. In seawater, however, copper
complexes with naturally occurring organic ligands are predomi-
nant. Dissolved organic copper complexes include those with
amino acids, carboxylic acids and humic acids. Substantial
organic-copper complexation may occur even in water with rela-
tively low organic content, and increases with decreasing pH and
increasing salinity. Chloride can strongly bind to Cu(I) and this
explains the presence of Cu(I) in seawater( 2 ).
The photoredox behavior of Cu(II) complexes, similarly to
those of Fe(III), is derived mostly from the reactive decay of their
LMCT states. Excitation to LMCT excited states can be attain-
able by direct sunlight, when the ligands coordinated to Cu(II)
are good enough electron donors. As a consequence of the reac-
tive decay of the LMCT excited state by inner-sphere electron
transfer, the Cu(II) central atom is reduced to Cu(I), whereas
the ligand or another available electron donor is oxidized to its
radical, for example:

CuIIðÞLL 2

hi

!

hvðÞLMCT

CuIþLL

þ ð 38 Þ

or

CuIIClx

hi 2 
x

!

hvðÞLMCT

CuIClx
 1

hi 2 
x

þCl ð 39 Þ

322 ZOFIA STASICKA