In-situ evolution of anodic TiO2 nanotubes to ammonium oxofluorotitanate mesocrystals and their conversion to mesocrystalline TiO2

Abstract

3D ordered superstructures of mesocrystalline NH4TiOF3 and (NH4)2TiOF4 are synthesized via in-situ evolution from anodic TiO2 nanotube arrays grown on the Ti metal substrate under high current density. As revealed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy characterizations, the obtained NH4TiOF3 and (NH4)2TiOF4 mesocrystals consist of well aligned nanoparticle subunits at atomic level and can be converted to TiO2 (anatase) mesocrystals with their original exterior shapes retained upon thermal annealing. Close examination suggests that NH4TiOF3 and (NH4)2TiOF4 mesocrystals form via a nonclassical crystal growth process involving fast oriented aggregation of particles assisted by electric field-dipole interaction.

Keywords

• Non-classical crystal growth
• Mesocrystal
• Ammonium oxofluorotitanates
• TiO2
• Electric field driven oriented attachment