inorganic chemistry

ABSTRACT

This review has been written in order to clarify fundamental
aspects of photocatalysis, an important subject in inorganic and
material chemistry, not to present a list of studies on photo-
catalysis reported so far, since it seems rather difficult to make
a complete review by introducing all or a large part of the
reported studies on photocatalysis of relatively long history. This
review is based on the author’s experience in studies on photo-
catalysis and topics are limited to so-called semiconductor photo-
catalysis; definition and examples of photocatalysis, its principle
and kinetics, visible light-induced photocatalysis, and design of
active photocatalysts are discussed in detail.

Keywords:Photocatalysis and catalysis; Photocatalytic activity;
Band structure and excitation; Energy conversion; Langmuir-
Hinshelwood mechanism; Electron–hole recombination; Quan-
tum efficiency; Physical property–activity correlation; Synergetic
effect.

I. Introduction

After the relatively long history of studies on photocatalysis, it
seems unnecessary to explain the importance of photocatalysis in
both fundamental and application aspects; for example, coatings
of window glass and exterior walls with photocatalysts have
already been commercialized worldwide due to its highly benefi-
cial effect of“self-cleaning”which enables the surface to be kept
clean under conditions of sunlight exposure and rain( 1 ). Since
results of many scientific studies on photocatalysis have been
reported, it seems rather difficult, at least for the author, to
make a complete review by introducing all or a large part of
the reported studies on photocatalysis, while, of course, success-
ful reviews (2,3) have been published by talented researchers in
this field. This review has been written in order to clarify funda-
mental aspects of photocatalysis, not to present a list of studies
on photocatalysis reported so far. Some of the aspects have not
been discussed so far as“common sense”in papers relating to
photocatalysis. This review is based on the author’s experience
in studies on photocatalysis for more than 25 years and topics
are therefore limited to so-called semiconductor photocatalysis
(Sections II.A and III.A), and consequently the author’s results
and interpretations are highlighted. It is the author’s pleasure

396 B. OHTANI