(Invited) The Inestimable Contributions of Akira Fujishima to Science and Technology: Photoelectrochemistry, Photocatalysis and Photoinduced Superhydrophilicity
Authors: Tryk Donald A. 
Published: December 2024

The first report of the photo-induced oxygen evolution reaction on UV-irradiated TiO2 was in 1969.1 That year, the results were also presented at the Annual Meeting of the Electrochemical Society of Japan. At the time, many people did not believe the results. This is a testament to their revolutionary character. It was not until the results were published in the Bulletin of the Chemical Society of Japan two years later and in Nature three years later that the ideas began to be accepted.2,3 The results are still recognized as being revolutionary and have been cited over 30,000 times, according to the Web of Science, and over 38,000 times, according to Google Scholar, earning it a place in the list of the 100 most highly scientific papers of all time. The results then became the subject of intense investigation in the early 1970s, with important confirmatory studies being published, for example, by Wrighton, et al.4 It became apparent that the band-gap of TiO2 was too large for the effective utilization of sunlight in water splitting, but, nevertheless, many researchers have been continuing to develop new types of semiconductors and compound structures. Thus, water can now be split effectively with sunlight.
In the meantime, Fujishima and coworkers began to make use of the oxidative power of TiO2 in photocatalytic self-cleaning and self-sterilization. This work has led to numerous basic studies, as well as applications, from surgical catheters to window glass, to whole buildings.5 Notably, photocatalytic coatings have recently been intensively developed for the decomposition of viruses by many researchers.
Twenty-five years after the original paper in Nature, a second ground-breaking paper appeared, this time on the phenomenon of photo-induced hydrophilicity.6 This phenomenon has some relationship to traditional photocatalysis but is distinct from it, although some researchers have claimed that they are in fact identical. This debate has continued up to the present, with fundamental surface science studies and theoretical calculations being carried out, but there is increasing recognition that it is a separate phenomenon, involving the photo-induced dissociation of water molecules at the TiO2 surface, greatly enhancing its hydrophilicity.
Thus, Fujishima’s work has given major impetus to the fields of artificial photosynthesis, the production of solar fuels, and photo-induced self-cleaning and anti-fogging, as well as having a tremendous impact on the development of antibacterial and antiviral coatings.
References

Fujishima, K. Honda, and S. Kikuchi, Kogyo Kagaku Zasshi, 72, 108 (1969).

Fujishima and K. Honda, Bull. Chem. Soc. Japan, 44, 1148-1150 (1971).

Fujishima and K. Honda, Nature, 238, 37-38 (1972).

S. Wrighton, D. S. Ginley, P. T. Wolczanski, A. B. Ellis, D. L. Morse, and A. Linz, Proc. Nat. Acad. Sci., 72, 1518-1522 (1975).

Zhang, D. Tryk, H. Irie, A. Fujishima, Editors, Handbook of Self-Cleaning Surfaces and Materials: From Fundamentals to Applications, Wiley-VCH (2023).

Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kojima, et al., Nature, 388, 431-433 (1997).