inorganic chemistry

(stationary)-state approximation is used to analyze the kinetics,
assuming forward reaction to give products and backward reac-
tion, that is, de-excitation. In such analyses, there may be no
rate-determining step.

V. Visible Light-Induced Photocatalysis

A. BACKGROUND

It has been claimed since the early stage of studies on photo-
catalysis that only one possible drawback of titania is its photo-
absorption wavelength range shorter than ca. 400 nm; titania
can absorb ultraviolet light included a little in solar radiation
( 29 ). Since solar radiation includes light of wavelengths from
280 to 4000 nm, use of photocatalysts that absorb light in visible
and near-infrared regions is highly desired. However, light of
longer wavelength has smaller energy, leading to a decrease in

Rate

Ea1

Ea3

Ea2

ΔG

Step 1 Step 2 Step 3 Step 4

Ea4

Rate-

determining

(a)

pc pc(e–-h+)

Light

Deactivation

= recombination

Redox

produdct(s)

(b)

FIG. 9. (a) Model interpreting a rate-determining step in a four-step
series reaction. Step 3 with largest activation energy determines the
overall rate. (b) Simplified scheme of photocatalytic reaction with a
photocatalyst“pc.”It is clear that this process is not a series reaction
since a“deactivation step”is included.

414 B. OHTANI