Ultrasmall Titania Nanocrystals and Their Direct Assembly into Mesoporous Structures Showing Fast Lithium Insertion

• Published in: Journal of the American Chemical Society Vol. 132; no. 36; pp. 12605 - 12611
• Main Authors: Szeifert, Johann M, Feckl, Johann M, Fattakhova-Rohlfing, Dina, Liu, Yujing, Kalousek, Vit, Rathousky, Jiri, Bein, Thomas
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15-09-2010
• Subjects: Lithium - chemistry; Molecular Structure; Nanoparticles - chemistry; Particle Size; Porosity; Surface Properties; Titanium - chemistry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja101810e

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 °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 m2/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.