From NH4TiOF3nanoparticles to NH4TiOF3mesocrystals: steric hindrance versus hydrophobic attraction of F127 molecules

Abstract

The formation of NH4TiOF3 mesocrystals can be largely manipulated by controlling the colloidal and chemical stabilities of NH4TiOF3 nanoparticles as the building blocks. The factors studied in the present work are temperature and the concentration of F127 (a triblock copolymer). At 23 °C and 35 °C, the presence of 10% F127 gives rise to the formation of submicron particles, whereas, a lower concentration of F127 results in submicron particles and aggregates, and a higher concentration produces a combination of NH4TiOF3 mesocrystals and submicron particles. The process is dominated by the formation of NH4TiOF3 mesocrystals at 4 °C, where the chemical conversion from NH4TiOF3 nanoparticles to TiO2 nanoparticles is significantly slowed down. A pancake-like conformation of F127 molecules on the hydrophilic particle surfaces is adopted to explain the concentration dependent steric effect and hydrophobic attraction imparted by their PPO chains. The TiO2 nanocrystals derived from calcination show superior photocatalytic performance, in comparison to TiO2 mesocrystals, due to the much higher specific surface area.