Microfluidic plasmonic packed-bed reactor (μPPBR) for photocatalytic water purification

Abstract

This M.Phil. study reports a novel microfluidic plasmonic packed-bed reactor (μPPBR) that is filled with Au-decorated TiO₂ microspheres with the aims to sensitize TiO₂ to visible light using localized surface plasmonic resonance (LSPR) and to also enhance the mass transfer inside the microfluidic reactor for high efficiency. Photodegradation of organic pollutants using sunlight has long been regarded as the idea technique for water decontamination, but the widely-used TiO₂ material is not responsive to visible light. Although different microfluidic reactors have been developed to study the reaction kinetics, their degradation efficiency in one-pass operation is often limited by the low mass transfer. To overcome these problems, this research stuffs Au/TiO₂ microspheres into a microchamber to form the μPPBR. The novelty of this work lies in the combined use of Au/TiO₂ microspheres and the packed-bed mode. This is the first demonstration of this kind of design. In this thesis, detailed discussions will be presented to cover the design and analysis of microfluidic reactors, the methodology and the experimental studies. In the first part, the design of the packed-bed microfluidic reactor are elaborated and then compared with the commonly-used film-mode microfluidic reactor. Theoretical analysis and COMSOL simulation have found that the μPPBR significantly enhances the mass transfer but at the cost of much increased pressure drop. In the second part, the preparation procedures of Au/TiO₂ microspheres are elaborated, and the fabrication processes of different microfluidic reactors are discussed. These serve as the methodology of this research. The last part of research presents the experimental results, including the material characteristics and the photodegradation efficiencies. It is found that the Au/TiO₂ microspheres are 2 - 3 times faster than TiO₂ microspheres, and the μPPBR is enhanced by 3 - 4 times as compared to the film-mode reactor. The combined use of Au/TiO₂ in the μPPBR enables an enhancement factor of 8 times as compared to TiO₂ in the film-mode reactor. In conclusion, this research has presented an original design of microfluidic reactor that seamlessly integrates the LSPR effect and the packed-bed mode of reactor. The new design has experimentally shown an enhancement factor of 8 in the photodegradation efficiency as compared to the TiO₂ film-mode reactor. This reactor can be further improved by optimizing the microsphere size and may be used for other photocatalytic applications such as photosynthesis and water splitting.