Wednesday, 15 September, 2010
Ultrasmall Titania Nanocrystals and Their Direct Assembly into Mesoporous Structures Showing Fast Lithium Insertion
J. M. Szeifert, J. M. Feckl, D. Fattakhova-Rohlfing, Y. Liu, V. Kalousek, J. Rathousky and T. Bein -
J. Am. Chem. Soc, 132 (36), pp. 12605-12611 (2010)
Ultrasmall and highly soluble anatase nanoparticles were synthesized from TiCl4 using tert-butyl alcohol as a new reaction medium. This synthetic protocol widens the scope of nonaqueous sol-gel methods to TiO2 nanoparticles of around 3 nm with excellent dispersibility in ethanol and tert-butanol. Microwave heating was found to enhance the crystallinity of the nanoparticles and to drastically shorten the reaction time to less than 1 h at temperatures as low as 50 degrees C. The extremely small size of the nanoparticles and their dispersibility make it possible to use commercial Pluronic surfactants for evaporation-induced self-assembly of the nanoparticulate building blocks into periodic mesoporous structures. A solution of particles after synthesis can be directly used for preparation of mesoporous films without the need for particle separation. The mesoporous titania coatings fabricated using this one-pot procedure are crystalline and exhibit high surface areas of up to 300 m(2)/g. The advantages of the retention of the mesoporous order with extremely thin nanocrystalline walls were shown by electrochemical lithium insertion. The films made using microwave-treated nanoparticles showed supercapacitive behavior with high maximum capacitance due to quantitative lithiation with a 10-fold increase of charging rates compared to a standard reference electrode made from 20 nm anatase particles.