Combustion synthesis of titania nanoparticles in a premixed methane flame

Previous studies have shown that titanium tetra-isopropoxide (TTIP) can be a substitute in the production of non-poisonous and inexpensive nanostructured titania (TiO2) particles. This study discusses the combustion characteristics of synthesized titania obtained while adding TTIP into the premixed methane/air flames. As the TTIP concentration increased, a bright yellow flame brush, representing a region of titania nanoparticles production, appeared on the tip of the flame's inner luminous cone. The crystal structure of the synthesized nanoparticles was analyzed using X-ray diffraction (XRD) and transmission electron microscope (TEM). The Barrett, Joyner, and Halenda (BJH) model was used to estimate the pore volume and pore size of the titania. Additionally, the specific surface area (SSA) of the synthesized titania nanoparticles was measured by a Brunauer-Emmett-Teller (BET) apparatus (Micromeritics ASAP 2020). The variation of the molar ratio (of oxygen-to-nitrogen) had an important influence on the temperature distribution and, accordingly, on the particle kinetics. It was found that in the flame temperature range from 1138 to 1290 K, the anatase content of the titania particles increased in direct proportion with the oxygen concentration. Moreover, high-purity anatase titania nanoparticles that were 20 nm in diameter were synthesized in methane/air flames with a TTIP concentration of about 0.26%. Overall, as the TTIP concentration increased, the flame temperature decreased, and it yielded a slightly higher percentage of rutile titania nanoparticles. The best titania macroporous-mesoporous structure was more preferable than the commercial Degussa P25 titania in terms of a higher percentage of anatase nanoparticles, a smaller mean particle diameter (Z-average), a higher BET SSA, and a larger pore volume and pore size. The photocatalytic properties of the flame-synthesized titania nanoparticles and commercial Degussa P25 were compared regarding the degradation of methyl orange. In the results, the flame-synthesized titania nanoparticles (ϕ = 1.0, TTIP = 0.32%, O2/N2 = 40/60) were more efficient in the removal of methyl orange.