Effect of Solvent on the Crystal Growth of One-Dimensional ZrO₂−TiO₂ Nanostructures

Previously we reported the synthesis of unique nanotubular bimetallic oxides, ZrO₂−TiO₂, in supercritical carbon dioxide (scCO₂). This study examines the role of the solvent on crystal growth by synthesizing the bimetallic nanomaterials using several common sol−gel solvents of varying dielectric strength, including scCO₂, hexane, xylenes, isopropanol, and ethanol. During synthesis, the gelation times, t_g, were measured. After synthesis, all materials were dried similarly in scCO₂ to remove the effect of synthesis from drying. The synthesized materials were subsequently characterized by several physicochemical techniques in order to assess the effect of the solvent on the morphology, porous structure, and thermal and crystallization behavior of the nanomaterials. Gelation times were found to follow a direct relationship with the dielectric constant of the solvent. Formation of nanotubular structure was found with scCO₂, whereas the other solvents gave primarily nanorod structures. Theoretical calculations were also performed on determining the solubility parameters of the sol−gel starting materials and bimetallic hexamer intermediates, showing that nanostructure was enhanced by lower dielectric constant solvents.