New approaches in lowering the gas-phase synthesis temperature of TiO2 nanoparticles by H2O-assisted atmospheric pressure CVS process

H2O-assisted atmospheric pressure chemical vapor synthesis is a modern economical process for the gas-phase synthesis of TiO2 nanoparticles. In the present work, the influence of synthesis temperatures (100–800 °C) on the phase structure, nanoparticle size, morphology, and agglomeration is investigated by transmission electron microscopy, selected area electron diffraction, X-ray diffraction, thermogravimetry, and differential thermal analysis. Down to 400 °C, crystalline TiO2 nanoparticles are synthesized and at 200 °C amorphous nanoparticles are formed. Therefore, a decrease in minimum synthesis temperature by more than 500 °C is achieved. In addition, the paper investigates the hypothesis that the high heat capacity of the H2O particles is responsible for the achieved decrease in synthesis temperature and for the dramatic decrease in size, coalescence, coagulation, and agglomeration of the nanoparticles. It is shown that the nanoparticles size is considerably higher for nanoparticles produced with gas-phase H2O particles in comparison to those produced with liquid-phase H2O particles, (average size 41 and 13 nm, respectively), because of the lower heat capacity of gas-phase H2O particles, thus confirming the hypothesis.