TiO₂ Nanorod-Derived Synthesis of Upstanding Hexagonal Kassite Nanosheet Arrays: An Intermediate Route to Novel Nanoporous TiO₂ Nanosheet Arrays

In this report, upstanding and nanoporous hexagonal TiO₂ nanosheet arrays were achieved via using kassite [CaTi₂O₄(OH)₂] as an intermediate. The process developed involved a TiO₂ nanorod-derived synthesis of upstanding hexagonal kassite nanosheet arrays and a transformation of the kassite to TiO₂. To the best of our knowledge, this is the first successful attempt to grow ordered hexagonal kassite nanosheet arrays. The as-obtained kassite nanosheets showed a single-crystalline nature with their <i>c</i>-axis parallel to the substrate. A stepwise study of the growth of the interesting hexagonal kassite nanosheet arrays was demonstrated. Upon hydrothermal treatment with diluted HNO₃ aqueous solution, the single-crystalline hexagonal kassite got converted to nanoporous rutile TiO₂, with shape preservation. The approach described in this study provides a novel method for the synthesis of kassite and TiO₂ nanosheet arrays and are ready for a variety of applications such as in catalytic or optoelectronic fields.