Sol-gel synthesis of linear Sn-doped TiO2 nanostructures

The sol-gel synthesis of linear Sn-doped TiO2 (TDT) nanostructures with high aspect ratios is reported. These binary metal-oxide nanostructures are readily accessed by treating titanium isopropoxide (Ti((OPr)-Pr-i)(4)) with appropriate quantities of acetic acid (AcOH) and Sn(OAc)(4) in heptanes to generate linear macromolecules that form nanofibers upon calcination. While these linear nanostructures are isolated at low R values (0.05-0.20), where R is defined as the molar ratio of Sn(OAc)(4) to Ti((OPr)-Pr-i)(4), axially directional growth is not favored at higher R values (0.30-0.50). Scanning and transmission electron microscope (SEM and TEM) imaging of the nanofibers revealed diameters in the 10-20 nm range and lengths in excess of 1 mm. Elemental mapping by STEM-EDS techniques indicates a homogeneous distribution of Sn ions throughout the linear TDT structures. The molecular intermediates that form during the early stages of the reaction were monitored using electrospray-ionization mass spectrometry to confirm the presence of metal-oxide clusters containing both Sn and Ti ions. These intermediates then undergo polycondensation reactions to form the final linear product, thereby indicating the homogeneous incorporation of Sn into the TiO2 lattice and rules out the possibility of independent SnO2 and TiO2 aggregates. Powder X-ray diffraction data indicate that pure TiO2 nanostructures are anatase when calcined at 500 degrees C, but show a propensity to adopt the rutile phase at progressively higher Sn concentrations.