(NH4)3TiOF5 mesocrystals grown by electric-field-assisted oriented-particle aggregation and their conversion to a TiO2 superstructure

This work reports an electrochemical synthesis of (NH 4 ) 3 TiOF 5 mesocrystals consisting of nanocrystalline building units, via oriented particle attachment driven by an external electric field. The obtained (NH 4 ) 3 TiOF 5 mesocrystals are octahedral in shape and can be converted to porous anatase TiO 2 , retaining their octahedral morphology after thermal annealing treatment. A distinctive evolution process for the (NH 4 ) 3 TiOF 5 mesocrystals with octahedral morphology is revealed, which includes the nucleation and growth of primary small octahedral particles, oriented aggregation of six primary octahedral particles into one large secondary particle, formation of mesocrystalline octahedrons by crystallographic fusion, dissolution of the octahedrons into small nanoparticles, followed by oriented aggregation of the dissolved nanoparticles to form micrometer-sized octahedrons. The alignment and subsequent oriented attachment of nanoparticles driven by an external electric field enable the rapid growth of (NH 4 ) 3 TiOF 5 mesocrystals within 40 s, compared with the tens of hours usually required for the growth of NH 4 TiOF 3 mesocrystals using a hydrothermal method.