Almost 40 years ago, we succeeded for the first time, in the photoelectrochemical decomposition of water without any applied electric power, by using TiO₂ as the anode. This discovery attracted worldwide attention and triggered enormous research activity in numerous laboratories to photoelectrochemically decompose water with semiconductors. The principles and measurements obtained with photoelectrochemical studies at semiconductor electrodes have led to the research activity on heterogeneous photocatalysis. Again, in 1997 we reported the novel photo-induced superhydrophilicity of TiO₂, and proposed the concept of self-cleaning surface based on the photocatalytic and superhydrophilic properties of TiO₂.
Today, TiO₂photocatalysis has shown numerous applications in air and water purification, self-cleaning materials, and medical science. Essential point of the photocatalytic reactions is related to nanomaterials.
Just recently we have studied new application for printing by use of strong decomposition power and wettability conversion of TiO₂ photocatalysis.
Offset printing, which is a familiar process in the industry, can be an excellent candidate for the application of the superhydrophilic-superhydrophobic pattern on TiO₂surface. In the present work, we have fabricated superhydrophilic-superhydrophobic printing plate, which is made from anodized aluminum, with the use of a TiO₂ photocatalyst. The fabrication process consists of three steps; (1) coating of TiO₂ photocatalyst on the printing plate, (2) modification of TiO2-coated printing plate surface with a self-assembled monolayer(SAM) of ODS or ODP, and (3) site-selective decomposion of the SAM by TiO₂ photocatalysis under UV irradiation with an aqueous ink-jet printing system. In the prepared superhydrophilic-superhydrophobic pattern, water was selectively entrapped in the superhydrophilic area. After dampening the surface of the printing plate with water, an ink pattern is formed on the superhydrophobic area with a line width of 200 µm. Moreover, the possibility of these applications of pattern to the offset printing has been investigated.