Bio-Inspired Titanium Dioxide Materials with Special Wettability and Their Applications

摘要

Titanium dioxide (TiO_2) is one of the most widely used nanomaterials in our daily life. In 1972, Fujishima and Honda reported the photo electrolysis of water into H_2 and O_2 utilizing an electrochemical cell in which the TiO_2 single-crystal electrode is connected with a Pt electrode.1 This is analogus with the natural photosynthesis that produces oxygen through oxidizing water and reducing carbon dioxide using sunlight, where solar energy is converted into chemical energy.~2 Since that time, photocatalysis has received considerable attention owing to its important applications in the conversion of light energy into useful chemical energy.~3 In 1997, Fujishima et al. first reported the photogeneration of a superamphiphilic (both superhydrophilic and superoleophilic, where the contact angle of water and oil on a surface is almost 0°, respectively) TiO_2 surface under UV light irradiation, showing self-cleaning and antifogging characteristics.~4 This breakthrough work expanded the research field of TiO_2 materials and marked the beginning of a new era in TiO_2-based self-cleaning materials. Since then, an important effort has been focused on the understanding of the fundamental mechanism of this novel function and on the development of selfcleaning materials for a wide range of applications in energy, environmental, and industrial fields, resulting in the generation of new markets. Although photocatalysis and photoinduced superhydrophilicity can take place simultaneously on the same TiO_2 surface, they are intrinsically different processes.5 In recent years, environmental pollution and damage on a global scale have emerged as a serious issue. The viable environmental cleanup has attracted a great deal of attention to achieve important breakthroughs in the design of advanced materials and in the development of new technology. Now, a variety of TiO_2-based materials have been commercialized arising from their unique photoinduced properties. Furthermore, these commercial products demonstrate their importance in the environmental cleanup.5-26