Furnace aerosol reactor (FuAR) synthesis, characterization and study of collisional-sintering growth of nanostructured pristine and doped titanium dioxide particles

Nanostructured titanium dioxide particles have been widely utilized as a photocatalyst. The control of primary particle size is crucial for its optimal performance. Sintering is one of key mechanisms for growth of primary particles in gas phase synthesis processes such as furnace aerosol reactors (FuAR). Dopants such as vanadium have also been popularly used to enhance photoactivity of titanium dioxide. However, dopants significantly alter the sintering rate of pristine titanium dioxide. In this work, sintering activation energy and pre-exponential factor have been estimated with a tandem differential mobility analyzer (TDMA). Most aerosol models assume a constant fractal dimension of agglomerates as they simulate collisional growth. However, the fractal dimension changes depending on the collision and sintering rates. A variable fractal dimension expression is obtained with respect to the ratio of the characteristic collision time to sintering time using a Brownian dynamics (BD) simulation. A new sintering equation based on geometry and neck growth rate has been developed because the current model underpredicts sintering rates in the initial stage. Particles synthesized by an aerosol method usually form agglomerates, that are represented by an equivalent mobility diameter. However, there are not sufficient studies relating the mobility diameter to the number and size of primary particles. Such an expression is established in this work, along with a scaling exponent to convert the mobility diameter to the agglomerate surface area. Synthesized pristine titania and iron- and vanadium-doped titania are characterized with X-ray diffraction (XRD) spectroscopy and high resolution transmission electron microscopy (HRTEM). As an application of synthesized particles, vanadium doped titania was activated by a corona-soft X-ray and demonstrated to be more active than pristine titania.