Low temperature crystallization of TiO2 in layer-by-layer assembled thin films formed from water-soluble Ti-complex and polycations

The multilayer films containing TiO2 nanoparticles were successfully fabricated by the alternative deposition of a water-soluble TiO2 precursor, titanium(IV) bis(ammonium lactato) dihydroxide (TALH), and positively charged polyelectrolytes utilizing electrostatic interaction for film formation. The deposited amounts of TALH and polycations were detected by quartz crystal microbalance (QCM). In the case of strong polycation, poly(diallyldimethylammonium chloride) (PDDA), the deposited amount of TALH was larger than that of the films formed with weak polycations. From the TEM observation, TiO2 nanocrystals were formed even in the as-deposited film, and the crystalline phases were composed of both anatase and TiO2(B). Two types of post-treatments for the films were employed to improve the photoactivity of TiO2 crystals. The hot-water treatment is much effective for the crystal growth of TiO2 in layer-by-layer (LbL) film. In addition, the evaluation of photocatalytic activity via the formation of I2 from KI aqueous solution with UV-irradiation also indicated the utility of hot-water treatment for the activation of TiO2 in LbL films.