Simple Protocol for Generating TiO2 Nanofibers in Organic Media

Titania nanofibers in high yields can be accessed by treating titanium isopropoxide (Ti((OPr)-Pr-i)(4)) With acetic acid (AcOH) in heptanes when R >= 4.2, where R = mol of AcOH/mol of Ti((OPr)-Pr-i)(4). Electron microscopic (SEM and TEM) images of the samples confirmed that high-aspect-ratio nanofibers with diameters in the 10-20 nm range are produced under these conditions, whereas agglomerated spherical nanoparticles are produced at R <= 3.8. Powder X-ray diffraction and UV-vis data confirm the anatase crystalline phase after calcination at 400 degrees C, with the progressive formation of the rutile phase upon heating to higher temperatures. N-2 physisorption analyses showed the calcined fibers prepared at R = 5.5 have surface areas of 95 m(2)/g. The self-assembly pathway leading to the nanofibers was delineated by in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy in tandem with electrospray ionization mass spectrometry (EST-MS). It was found that the hexanuclear building block, Ti6O6(OAc)(6)((OPr)-Pr-i)(6) (TAC1), is formed during the initial stages of the reactions, and that the axially ligated isopropoxide ligands of this complex are subsequently hydrolyzed to facilitate the one-dimensional condensation of the macromolecules at R >= 4.2. Incomplete hydrolysis at lower acid ratios impedes this axial growth, resulting in spherical nanoparticles.