Performance Of TiO2-based Porous Photocatalysts For Removal Of Indoor VOCs

Adsorption and photodegradation are key steps in indoor air purification. Micropores have been introduced to TiO2nanocatalysts in order to enhance the adsorption of the pollutant on the photocatalyst surface, thereby increasing the utilization of the photo-induced electron-hole pairs. Two different nanocomposites, anatase microporous TiO2and amorphous microporous TiO2, have been synthesized under mild hydrothermal conditions using dodecylamine/dodecyl-2-pyridinyl-methylamine as pore-forming agents and varying temperature of preparation. Samples synthesized at different conditions provided interesting insights into the impact of crystallinity, valence of surface elements, and micropore area on the removal efficiency of gas-phase organic pollutants. Among the two, amorphous microporous TiO2had the largest micropore surface area of493m2·g-1but amorphous phase, while anatase micorporous TiO2had both a relatively large micropore urface area of258m2·g-1and anatase crystal structure. Toluene and cyclohexane were chosen as two models of hydrophilic and hydrophobic air pollutants. Experiments were performed in a single-pass reactor under a variety of experimental conditions, such as varying partial pressures of toluene, contact times, and relative humidities of the mobile gas phase, in order to approximate the realistic conditions. The equilibrium-adsorption-amount of toluene and cyclohexane over amorphous microporous TiO2were36.8and8times higher than those of P25, respectively. Moreover, the amorphous microporous TiO2also showed efficient self-recovery ability. Among the two prototype catalysts, anatase micorporous TiO2showed the highest removal and mineralization efficiency. The adsorption capacity and photocatalytic removal efficiency are controlled by the micropore surface area, concentration of surface TiⅡ andTⅢ, and the crystallinity of the photocatalyst. Besides, to protect the surface active sites of TiO2from being infected by the particles generally existed in atmosphere, porous-SiO2-encapsulated TiO2was developed. The pore size of outside SiO2shell can be well controlled between5-10nm. The inside TiO2nanoparticles aggregated together to form porous profile thereby generating relatively large amount of reactive sites. The results showed that the SiO2shell didn’t reduce the photocatalytic activity of inner TiO2and shield the electric charge on the TiO2surface.