Manipulating the formation of NH 4TiOF 3 mesocrystals: Effects of temperature, surfactant, and pH

Abstract

There are two main competitive processes involved in the formation of NH 4TiOF 3 mesocrystals. One leads to the assembly of individual NH 4TiOF 3 nanocrystals and the subsequent formation of NH 4TiOF 3 mesocrystals. The other converts the NH 4TiOF 3 nanocrystals into TiO 2 (anatase) nanoparticles and results in the subsequent formation of TiO 2 aggregates. Surfactant (Brij 58) molecules appear to facilitate the mesoscale assembly of NH 4TiOF 3 nanocrystals into NH 4TiOF 3 mesocrystals via the interaction of their hydrophobic tails. Elevated temperature and higher solution pH (adjusted by ammonia solution) increase the conversion rate of NH 4TiOF 3 nanocrystals into TiO 2 (anatase) nanoparticles. This conversion process reduces the amount of NH 4TiOF 3 nanocrystals available for the mesoscale assembly and consequently increases the pore volume of the resultant NH 4TiOF 3 mesocrystals. Fluorination and {001} facets affect the photocatalytic performance of the calcined products (anatase TiO 2) of the NH 4TiOF 3 mesocrystals. The present study demonstrates the key parameters that control the formation and stability of NH 4TiOF 3 mesocrystals and the photocatalytic behavior of nanocrystalline TiO 2 derived from the mesocrystals. © 2012 American Chemical Society.