Kinetic effects of polymorphs and surface areas on adsorption and photocatalytic decomposition of acetaldehyde on titania

Abstract Adsorption and photocatalytic decomposition behaviors of gas-phase acetaldehyde (CH3CHO), together with carbon dioxide (CO2) formation have been measured for pure titania (TiO2) powders with three types of polymorphs (anatase, brookite, and rutile) under UV-light illumination, and assessed by a kinetic model that takes into account the immediate decomposition of CH3CHO attached on the surface, and the gradual decomposition of CH3CHO adsorbed on the surface. Experimental data are well reproduced by the present model, highlighting how adsorption-related pathways markedly contribute to overall CH3CHO removal kinetics even for pure titanias. Although the initial removal rate depends on the surface area, which affects the adsorption capacity, it is suggested that specific surface area-based adsorbability and decomposition reactivity are enhanced by heightened crystallinity. Our kinetic analysis demonstrates that anatase exhibits the highest photocatalytic activity as a result of superior adsorbability, as well as superior decomposition reactivity, compared to other polymorphs.