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

Abstract H 2 O-assisted atmospheric pressure chemical vapor synthesis is a modern economical process for the gas-phase synthesis of TiO 2 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 TiO 2 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 H 2 O 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 H 2 O particles in comparison to those produced with liquid-phase H 2 O particles, (average size 13 and 41 nm, respectively), because of the lower heat capacity of gas-phase H 2 O particles, thus confirming the hypothesis.