Study of electron transfer processes in plasmonic photocatalysis
5 December 2017
Stadscampus, Willem Elsschotzaal - Prinsstraat 13 - 2000 Antwerpen (route: UAntwerpen, Stadscampus
Organization / co-organization:
Department of Bioscience Engineering
Silvia Lenaerts, Johan Martens & Sammy Verbruggen
PhD defence Maarten Keulemans - Faculty of Science, Department of Bioscience Engineering
Over the past few years, the use of plasmonics to improve the photocatalytic efficiency of titanium dioxide (TiO2) has gained a lot of interest in the scientific community. By modifying the TiO2 photocatalyst with noble metal nanoparticles displaying surface plasmon resonance, its activity under both UV and a broad range of visible light can be enhanced substantially. Surface plasmon resonance is an optical phenomenon that gives the noble metal nanoparticles unique properties enabling them to manipulate, concentrate and amplify light at the nanoscale. The nanoparticles essentially act as highly efficient light absorbers, capturing visible light energy and transferring it to the TiO2 photocatalyst to activate it. Combining the fields of plasmonics and photocatalysis thus yields plasmonic photocatalysis. This is a novel field of science with many unanswered questions. A lot of progress is therefore still being made toward fully understanding its interesting features. This thesis aims to study different aspects of plasmon mediated photocatalysis. In this regard, emphasis is put on further investigating electron transfer processes.
In first instance, a new approach is evaluated to improve the photocatalytic efficiency of commercially available TiO2 photocatalysts under sunlight irradiation. This is achieved by tailoring the photoresponse of the TiO2 photocatalyst to match the solar spectrum through the use of gold-silver alloy nanoparticles. Electron transfer processes are postulated to play an important role in the activity enhancement. Therefore, effort is made in gaining more fundamental knowledge in these electron transfer processes occurring in the developed plasmonic photocatalysts. To this end, electron paramagnetic resonance is used as a fundamental, high-end characterization technique to investigate electron transfer between the plasmonic nanoparticle and the photoactive TiO2 support. Experimental evidence for visible light induced energetic electron transfer from the plasmonic nanoparticle to the TiO2 photocatalyst is provided thus substantiating the previously made hypothesis. Consecutively, more widely applicable and inexpensive characterization methods using different probe molecules are developed and tested. Finally, all previous knowledge is combined to obtain a plasmonic photocatalyst that can potentially be used as a self-cleaning coating in real life applications.
In conclusion, various aspects of plasmon modified TiO2 photocatalysis are investigated with a focus on unravelling the underlying mechanisms responsible for the plasmonic enhancement. We are hopeful that the research presented in this work leads to a better understanding and novel insights in this fairly new and interesting research domain.