The crystal phase and shape of ZrO2 nanoparticles were finely tuned by mediating the hydrolysis rate of zirconium cations and using sodium oleate as the capping agent under hydrothermal conditions. Pure monoclinic ZrO2 nanorods with a diameter of ~3 nm and length of 30–40 nm were obtained at a lower pH value of 9.4; whereas monodispersed ZrO2 particles of ~4 nm with mixed monoclinic and tetragonal phases were formed at a higher pH value of 11.4. Their formation mechanism was discussed in terms of the hydrolysis rate of the zirconium cations and the structure-directing role of the oleate species. The monoclinic ZrO2 nanorods showed prominent blue-green fluorescence under excitation by an ultraviolet lamp (365 nm) because of the presence of a large number of oxygen-vacancy defects.

β-FeOOH nanorods of 40 nm wide and 450 nm long were fabricated through precisely regulating the hydrolysis kinetics of Fe3+ in polyethylene glycol and the concentration of Cl- as the structure-directing agent. Detailed structural and chemical analyses of the intermediates during the synthesis identified that the strong interaction between PEG and Fe3+ modulated the hydrolysis kinetics of Fe3+ and prevented the aggregation of β-FeOOH nanorods; while Cl- provided sufficient nucleation sites, stabilized the hollow channel of β-FeOOH, and more importantly induced the growth of the nanorods along [001] direction.

Anatase TiO2 nanosheets exposing 74% of {001} facets and nanospindles exposing 81% of {101} facets were hydrothermally synthesized with the aid of F− and CH3COO−, respectively. Upon vanadia loading at a monolayer amount level, the {001} facets on TiO2 nanosheets favored the deposition of octahedral vanadia species, but the {101} facets on TiO2 nanospindles resulted in the formation of tetrahedral vanadia species. The shape effect of TiO2, in terms of its predominantly exposed crystal facets, on the catalytic performance of VOx/TiO2 samples for selective reduction of NO with NH3 was examined. The octahedral vanadia species on TiO2 nanosheets showed a significantly higher activity than the tetrahedral vanadia species on TiO2 nanospindles.

Anatase TiO2 truncated bipyramids that dominantly exposed the reactive {001} facet were hydrothermally synthesized using vanadia as the structure-directing agent. The exposed fraction of the {001} facet approached 53% upon adjusting the V/Ti molar ratio of the synthetic solution. Mechanistic investigation, together with control experiments, verified that vanadia stabilized the {001} facet and induced the construction of the truncated bipyramids. After calcination at 723 K in air, the resulting VOx/TiO2 truncated bipyramids effectively catalyzed the selective reduction of NO by ammonia.

Polymorphous transformation of rod-shaped γ-Fe2O3 was applied to fabricate Fe3O4/Fe2O3 nanorods. Hydrogen reduction of γ-Fe2O3 nanorods at 350 °C yielded Fe3O4 nanorods with similar size; re-oxidation of the resulting Fe3O4 nanorods produced γ-Fe2O3 at 500 °C and α-Fe2O3 nanorods at 600 °C. When applied to catalyze selective reduction of NO with NH3, the activity followed the order γ-Fe2O3 > γ-Fe2O3-500 > α-Fe2O3 > Fe3O4, which was well correlated with their crystalline structures. The superior performance of γ-Fe2O3 nanorods was attributed to the simultaneous exposure of Fe3+ and O2−, which favoured the adsorption and activation of NH3 and NO molecules.

Anatase TiO2 hollow nanosheets with a width of 550 nm, a thickness of 100 nm, and a hole diameter of 350 nm were hydrothermally fabricated in an aqueous solution containing NH4VO3, HF, and HCl at an appropriate composition. Structural analyses on the products obtained at different intervals during the synthesis revealed that the formation of the anatase TiO2 hollow nanosheets consisted of three steps: oriented assembly of square-like NH4TiOF3 nanoparticles, topochemical conversion of NH4TiOF3 to anatase TiO2, and selective etching by F− on the flat nanosheets. The fluorine anion was involved in the formation of NH4TiOF3 as the key intermediate, it directed the construction of the nanosheet, and participated in the etching process to generate the hollow structure. The resultant anatase TiO2 hollow nanosheets exhibited a rather high thermal stability, maintaining the anatase crystallite structure and the hollow shape up to 1073 K.

Anatase TiO2 nanosheets exposing 74% of {001} facets and nanospindles exposing 81% of {101} facets were hydrothermally synthesized with the aid of F− and CH3COO−, respectively. Upon vanadia loading at a monolayer amount level, the {001} facets on TiO2 nanosheets favored the deposition of octahedral vanadia species, but the {101} facets on TiO2 nanospindles resulted in the formation of tetrahedral vanadia species. The shape effect of TiO2, in terms of its predominantly exposed crystal facets, on the catalytic performance of VOx/TiO2 samples for selective reduction of NO with NH3 was examined. The octahedral vanadia species on TiO2 nanosheets showed a significantly higher activity than the tetrahedral vanadia species on TiO2 nanospindles.