TiO2 nanopowders via radio-frequency thermal plasma oxidation of organic liquid precursors: Synthesis and characterization

TiO2 nanopowders have been synthesized via Ar/O2 thermal plasma oxidation of titanium butoxide (TBO) solutions stabilized with diethanolamine (DEA). Experiments were conducted by varying the O2 input in the plasma sheath (10–90 L/min) and the DEA/TBO molar ratio (R), while keeping the plasma generation power at 25 kW and the reactor pressure at 500 Torr. The resultant powders are mixtures of the anatase and rutile polymorphs in the studied range, whose anatase content and crystallite size exhibit weak dependence on the O2 input at a fixed R. Increasing R decreases the anatase content, signifying the role of CO gas, generated via oxidation of the organic precursor, on the phase structure. FE-SEM and TEM analysis show that the resultant powders contain majority of nanoparticles (<50 nm) and some large spheres (>100 nm), whose size and/or number tends to decrease at a higher O2 input, leading to gradually increased specific surface area. Raman spectroscopy reveals no significant differences in the crystallite size and oxygen-vacancy concentration of the nanocrystals by varying the O2 input.