New insight into reaction mechanisms of TiCl4 for the synthesis of TiO2 nanoparticles in H2O-assisted atmospheric-pressure CVS process

Abstract Crystalline anatase TiO2 nanoparticles were synthesized in the gas phase using an H2O-assisted atmospheric-pressure CVS process. Simultaneous oxidation/hydrolysis of TiCl4 in the H2O-assisted APCVS process demonstrates the feasibility of facile fabrication and the designed synthesis of TiO2 nanoparticles in atmospheric pressure. Kinetics and thermodynamics studies of TiCl4 reactions in the gas phase illustrated oxidation or hydrolysis domination theoretically and were confirmed by experimental runs. Effects of H2O/O2 ratio on the reactions mechanisms, phase formation, size characteristics, morphology, and purity of TiO2 nanoparticles were experimentally studied using various analytical techniques including TEM, XRD, SAED, and TG-DTA. The synthesized particles were significantly finer with higher crystallinity than those produced by the solitary oxidation process. The average size of TiO2 nanoparticles was 12 ± 4 nm under simultaneous oxidation/hydrolysis, while that was 34 ± 5 nm without hydrolysis. Hydrolysis dominates in lower temperatures caused by lower activation energy and higher kinetics of hydrolysis reaction.