Abstract
By utilizing the pores of carbonaceous materials as a kind of nanoreactor, nanosized titania (TiO2) was prepared. The carbon materials acted as a support matrix for obtained titania nanostructures, which were immobilized on the internal surface. The precursor titanium tetraisopropoxide (TTIP) was first adsorbed in the pores of the carrier material. Titania was subsequently formed within the carrier pores by flash pyrolysis. Space confinement of the pores of the carrier was successfully applied to obtain only nanosized titania formed exclusively at the desired place inside the pores. On the other hand, transport resistance in the small pores and rapid heating helped to maximize titania yields because of quickly reaching a temperature regime where the reaction rate of the precursor exceeded its diffusive flux out of the carrier pores. With this method, titania loadings as high as 14 wt% were achieved. Obtained titania existed as monodisperse nanoparticles of 5 to 8 nm in diameter. The nanoparticles were single-crystalline of both anatase and rutile phases. Process parameters were investigated to clarify the optimum operation mode of the nanoreactor for maximum product yields. The titania yield was found to increase exponentially with rising reaction temperature. Rapid heating allowed for improving the titania yield significantly and was crucial to obtain nanoparticles of a good quality, i.e., narrow size distribution and good dispersion. The pore structure of the carrier material had a notable effect on the titania yield, i.e., the yield at very high temperatures in an ordered pore system were higher than in a random pore system. By variation of the precursor loading and changing the reactant, mass transport mechanisms in the pores could be clarified.
