inorganic chemistry

that transmit light of wavelength longer than a certain limit, that
is,“cut-off filters.”By using a number of filters with different cut-
off wavelengths, a plot of apparent quantum efficiency against
the cut-off wavelengths can be obtained, and this“pseudo-action
spectrum”seems like a“true”action spectrum obtained by the
above-described monochromatic irradiation. However, those are
completely different; a pseudo-action spectrum is an integrated
(from longer to shorter wavelengths) form of a“true”action spec-
trum based on the assumption that light intensity is constant in
the whole range of irradiation, because of the difference in irradia-
tion wavelength region (Fig. 12). Consequently, the corresponding
action spectrum should be estimated by differentiation of the
pseudo-action spectrum; a horizontal part in a pseudo-action spec-
trum (Fig. 12), if any, shows that apparent quantum efficiency at
the wavelength is negligible even if an appreciable value is seen
in the pseudo-action spectrum.

D. COCATALYSTLOADING FORMULTIPLEELECTRONTRANSFER

As has been discussed inSection III.E, a photocatalytic reac-
tion can proceed if the CB bottom and VB top are more cathodic
and anodic than the standard electrode potentials of electron
acceptors and donors, respectively. Therefore, band-edge position

Action spectrum

Pseudo-action

spectrum

Wavelength

Apparent quantum

efficiency

FIG. 12. Examples of action and pseudo-action spectra for photoin-
duced reaction by an ordinary semiconductor photocatalyst (shorter
wavelength) and an organic dye (longer-wavelength peak). A pseudo-
action spectrum taken by cut-off filters corresponds to integration of
the“true”action spectrum from the longer-wavelength side.

PHOTOCATALYSIS BY INORGANIC SOLID MATERIALS 419