Synthesis of Rutile-Phase SnxTi1-xO2 Solid-Solution and (SnO2)x/(TiO2)1-x Core/Shell Nanoparticles with Tunable Lattice Constants and Controlled Morphologies

We report the solvothermal synthesis of SnxTi1-xO2 solid-solution and (SnO2)(x)/(TiO2)(1-x) core/shell nanoparticles with tunable lattice parameters and morphologies over the range of 0 <= x <= 1. The products are characterized by transmission electron microscopy, powder X-ray diffraction, and and solid-state nuclear magnetic resonance spectroscopy. Rutile-phase particles with solid-solution or core/shell architectures are synthesized by combining titanium isopropoxide [Ti(O-i-Pr)(4)] with Sn-containing precursors (SnCl4 or SnO2 nanoparticles, respectively) to favor rutile crystal growth over the typically observed anatase-phase TiO2. The transition from the anatase to the rutile TiO2 phase is associated with increasing concentration of the Sn precursor. In the first case, we propose that the mixing of molecular Ti(O-i-Pr)(4) and SnCl4 precursors leads to the formation of a SnxTi1-xO2 solid solution which preferentially crystallizes in the rutile phase due to thermodynamics. In the second case, we propose that the rutile SnO2 nanoparticles act as nucleation sites for the heteroepitaxial growth of rutile TiO2, lowering the energy barrier for particle growth and generating (SnO2)(x)/(TiO2)(1-x) core/shell particles. The particle morphology and polydispersity are also altered systematically by varying the Ti/Sn ratio of the reactants, with particle elongation normal to the [110] direction observed for higher Sn concentrations. In the absence of Ti precursor, SnO2 nanowires with diameters < 5 nm are formed from SnCl4 under the reaction conditions.