Mesocrystals are an interesting class of nanomaterials, similar to colloidal crystal assemblies but differing by processing superstructures of vectorially (rather than randomly aligned) non-spherical nanocrystals. The nearly perfectly-ordered nanocrystalline subunits results in single-crystal-like electron diffraction patterns. Mesocrystals and their syntheses also provide a challenge to accepted views on crystal growth as is typically described by a process of nucleation and growth; and/or Ostwald ripening. Uniform mesocrystals of anatase TiO₂ have been prepared by a topotactic transformation from NH₄TiOF₃. Mesocrystals of NH₄TiOF₃ were synthesised from an aqueous solution containing (NH₄)₂TiF₆ and H₃BO₃ in presence of Brij series surfactants at room temperature. The exterior shapes of NH₄TiOF₃ mesocrystals can be tuned by adjusting the reaction parameters including: reagent concentration, reaction time, reaction temperature and rate of stirring. The formation of the mesocrystals of NH₄TiOF₃ proceeds via self-assembly process involving non-classical kinetically driven processes and amorphous intermediates. By sintering in air at 450 ^oC or washing with H₃BO₃ solution at ambient temperatures, the NH₄TiOF₃ mesocrystals can be converted to anatase TiO₂ mesocrystals by self-templated topotaxial conversion, thus retaining their original architecture.

SEM (a & b) and TEM (c) images of NH₄TiOF₃ mesocrystals

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1. Continuous Flow Supercritical Fluid MOCVD of Cu and Ag Thin Films: Reactor Design and CFD Modelling.