inorganic chemistry

whereas the 1.1% and 4.0% surface modified counterparts after
420 min exhibited 10% and 50% degradation, respectively (Fig. 5).
The superior activity of modified titania was demonstrated
also when the degradation of 4-CP was conducted with outdoor
sunlight. Surprisingly, 2.0%H 2 [PtCl 6 ]/TH was more active than
P25. This higher reactivity was even more pronounced when
the solar irradiation was replaced by artificial UV light. 2.0%
H 2 [PtCl 6 ]/TH induced 90% degradation already after 12 min,
the time by which only 50% were degraded byP25. In the case
of 4.0%H 2 [PtCl 6 ]/TH only traces of unreacted 4-CP could be
detected after this irradiation time.

D. MECHANISM

Since the chloroplatinate component is the light absorbing
species, we proposed the primary photoprocess to be a homolytic
PtCl cleavage affording a PtIII intermediate and an adsorbed
chlorine atom, by analogy with the known photochemistry of
hexachloroplatinate in solution(29,35). Electron injection from
the platinum(III) complex into the titania conduction band
reforms PtIV. Thus, the reductive and oxidative centers become
spatially separated rendering charge recombination less proba-
ble. The trapped conduction band electron reduces oxygen
to superoxide and finally hydroxyl radicals as evidenced by

0 60 120 180 240 300 360 420

0.5

0.6

0.7

0.8

0.9

1.0 a

c

b

4-CP,

c/

c^0

Time (min)

FIG. 5. Diffuse indoor daylight induced degradation of 4-CP in
the presence ofTHandP25(a), 1.1%H 2 [PtCl 6 ]/P25 (b), 4.0%H 2 [PtCl 6 ]/
TH (c).

VISIBLE LIGHT PHOTOCATALYSIS 383