Tailoring nanobranches in three-dimensional hierarchical rutile heterostructures: A case study of TiO₂-SnO₂

We employed HNO₃ as a hydrolysis control agent and developed three-dimensional (3D) hierarchical rutile heterostructures (TiO ₂-SnO₂) with a high-density, uniform, and epitaxial TiO₂ nanobranch tailored by a facile CBD method at a low temperature (∼50 °C). By investigating the influence of acids such as HNO ₃, HCl, H₂SO₄, and HCOOH on the formation of TiO₂ nanobranches on SnO₂ nanobelts (NBs), we demonstrate that the rate of crystal growth can be promoted by HNO₃ and that the poor ligand affinity of NO₃^- and the total charge variation of the Ti complex by H⁺ alter the precipitation rates, eventually controlling the length of the TiO₂ nanorods. Additionally, it was found that short and long TiO₂ nanorods were generated via the mechanism of diffusional- and reaction-controlled growth under moderate and high concentrations of HNO₃, respectively. TiO₂ nanorods grew epitaxially along the [001] direction on all four sides of SnO₂ NB like the spokes of a wheel. This was attributed to the minimization of surface energy and lattice mismatch. This facile, surfactant-free, and low-temperature synthetic strategy may provide an alternative route for fabricating uniform and length-controlled nanobranches in 3D heterostructures.