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

Highlights: • H₂O-assisted APCVS process was used for the synthesis of anatase TiO₂ nanoparticles. • TiO₂ nanoparticles were synthesized via simultaneous oxidation/hydrolysis of TiCl₄. • Kinetics and thermodynamics studies give new insight into TiCl₄ reaction mechanisms. • Effects of different H₂O/O₂ ratios were studied theoretically and experimentally. • Simultaneous TiCl₄ oxidation/hydrolysis results in higher crystallinity and purity. 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.