Size effects in gas-phase photo-oxidation of trichloroethylene using nanometer-sized TiO2 catalysts

Gas-phase photocatalytic oxidation is an attractive technology for the degradation of VOC, and TiO2 is the typically used environmental photocatalyst for the oxidation of gaseous or aqueous organic pollutants. A modified sol-gel method was developed to prepare TiO2 catalysts, which were characterized by XRD, transmission electron microscopy, and N2 physi-adsorption techniques. The effects of synthesis parameters (titanium isopropoxide (TIP) concentration, H2O concentration, H2O/TIP ratio, and TIP addition rate) were studied. Controlled thermal and/or hydrothermal treatments followed the sol-gel preparation to transform the amorphous TiO2 to crystalline anatase. The modified sol-gel method provided precise control over the primary and secondary particle sizes of TiO2 catalyst with their crystalline-phase structure and morphology. Changing the H2O concentration during the hydrolysis of TIP, produced amorphous TiO2 gel spheres having well-defined morphology and particle size (≥ 2.3 nm). The primary particle (crystal) size dictated the surface area of the TiO2 catalyst, while the secondary particle (aggregate) size had no effect on the surface area. Reaction studies using gas-phase photooxidation of trichloroethylene over anatase TiO2 catalysts prepared with crystal and aggregate sizes of 2.3-30 and 100-900 nm, respectively, showed that both the primary and secondary particle sizes of TiO2 affect the catalytic activity.