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.
Highlights
Advanced oxidation processes (AOPs) form a group of modern chemical technologies that rely on the generation of radical species and are considered to have high prospects for the oxidation, discoloration, mineralization, and degradation of organic pollutants [1,2]
Photocatalysis is an example of an AOP that has been effectively applied for the treatment of highly polluted
This study addressed the photocatalysis performance of suspended catalysts in an aggregated state
Summary
Advanced oxidation processes (AOPs) form a group of modern chemical technologies that rely on the generation of radical species and are considered to have high prospects for the oxidation, discoloration, mineralization, and degradation of organic pollutants [1,2]. This research has focused on the materials aspects such as the structural properties (e.g., surface area, particle size, crystal composition, porosity) [8,11] of pristine or modified photocatalysts [2,5,12]. Many of these laboratory-scaled apparatus are inappropriate to be applied in well-defined conditions, making the application with available pilot photoreactors challenging. While the higher photocatalytic activity of fine, primary particles (as a result of the larger surface area) has been investigated [4,16,17,18], the behavior and properties of the aggregates is not well understood
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