Design of Organic-Free Superhydrophobic TiO 2 with Ultraviolet Stability or Ultraviolet-Induced Switchable Wettability.

Superhydrophobic TiO 2 with great application potential is mainly obtained by surface modification with low surface energy organics, which is easily degraded under sunlight irradiation, which results in the loss of superhydrophobic properties. Herein, we developed a room-temperature pulsed chemical vapor deposition (pulsed CVD) method to develop amorphous TiO 2 -deposited TiO 2 nanoparticles. The ultraviolet stability/ultraviolet-induced reversible wettability switch had been simultaneously realized by different and controllable deposition cycles of amorphous TiO 2 . The superhydrophobic properties of the organic-free TiO 2 were determined by the micrometer-nanometer-sub-nanometer multiscale structure, the multiscale pore structure, and the large Young's contact angle resulting from carboxylic acid adsorption. Also, we found that the adsorption rate and adsorption stability of oxygen and water at the surface oxygen vacancies were the key to facilitate the reversible switching between superhydrophilic and superhydrophobic states, which was well demonstrated by experimental characterization and theoretical simulation. In addition, we also found that the resistance of dense amorphous TiO 2 films on the TiO 2 surface to the migration of photogenerated electrons and holes was the key to maintain the stable superhydrophobic properties of superhydrophobic TiO 2 under ultraviolet illumination. The powders were strongly ground and the coating surface was rubbed on the surface of the sandpaper, which still maintained superhydrophobic properties, providing favorable conditions for the application of superhydrophobic TiO 2 . This work modulates the ultraviolet stability and dark/ultraviolet-induced switchable superhydrophobicity/superhydrophilicity of coated TiO 2 by simply adjusting the number of deposition times in a pulsed CVD process for the first time, thus contributing to the development of organic-free superhydrophobic TiO 2 .