title: Impact of ultrasonic dispersion on the photocatalytic activity of titania aggregates.
abstract: The effectiveness of photocatalytic materials increases with the specific surface area, thus nanoscale photocatalyst particles are preferred. However, such nanomaterials are frequently found in an aggregated state, which may reduce the photocatalytic activity due to internal obscuration and the extended diffusion path of the molecules to be treated. This paper investigates the effect of aggregate size on the photocatalytic activity of pyrogenic titania (Aeroxide(®) P25, Evonik), which is widely used in fundamental photocatalysis research. Well-defined and reproducible aggregate sizes were achieved by ultrasonic dispersion. The photocatalytic activity was examined by the color removal of methylene blue (MB) with a laboratory-scale setup based on a plug flow reactor (PFR) and planar UV illumination. The process parameters such as flow regime, optical path length and UV intensity are well-defined and can be varied. Our results firstly show that a complete dispersion of the P25 aggregates is not practical. Secondly, the photocatalytic activity is not further increased beyond a certain degree of dispersion, which probably corresponds to a critical size for which UV irradiation can penetrate the aggregate without significant obscuration.
authors.affiliation: Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany; School of Chemical Engineering, Hanoi University of Science and Technology, 10000 Hanoi, Vietnam.
authors.forename: Hoai Nga
authors.initials: HN
authors.lastname: Le
authors.affiliation: Institute of Process Engineering and Environmental Technology, TU Dresden, 01069 Dresden, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Babick
authors.affiliation: Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Kühn
authors.affiliation: School of Chemical Engineering, Hanoi University of Science and Technology, 10000 Hanoi, Vietnam.
authors.forename: Minh Tan
authors.initials: MT
authors.lastname: Nguyen
authors.affiliation: Institute of Process Engineering and Environmental Technology, TU Dresden, 01069 Dresden, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Stintz
authors.affiliation: Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany; Dresden Center for Computational Materials Science (DCCMS), TU Dresden, 01062 Dresden, Germany; Center for Advancing Electronics Dresden, TU Dresden, 01062 Dresden, Germany.
authors.forename: Gianaurelio
authors.initials: G
authors.lastname: Cuniberti
keywords: AOPs; reaction rate constant; turbidity; ultrasonic energy; wastewater treatment