Organic semiconductors supported on silica nanospheres for photocatalytic application

Student thesis: Doc typesDoctor of Sciences

Abstract

Nowadays, there is a growing interest in the scientific community to find alternative synthetic methodologies for the development of sustainable chemical processes. In this regard, visible light-mediated metal-free photocatalytic transformations have emerged as an efficient and sustainable tool of organic synthesis. Several catalytic reactions, such as dehalogenation of different haloarenes, Aza-Henry or C-H arylation reactions, have already been achieved using this tool under homogeneous conditions. These organic transformations can be triggered by organic dyes, which play the role of photocatalysts (PC). The isolation of PC from the reaction mixture is often complicated, which makes the catalyst difficult to reuse in consecutive cycles. To overcome this problem, the development of next-generation reusable PC becomes a subject of big importance. This thesis arises in order to develop such a reusable heterogenized photocatalyst, suitable for several important organic transformations.

In this work, recently engineered organic semiconductors, namely peri-xanthenoxanthene mono- and diimides (PXXMI and PXXDI) were synthesized and covalently grafted onto mesoporous silica nanospheres. The obtained solids were mesoporous, luminescent and fluorescent, which was proven by various techniques. They were successfully employed in the photocatalytic debromination reaction and the photocatalytic C-H arylation of different heteroarenes. Their catalytic performances were compared to unsupported dyes in homogeneous conditions, revealing their outstanding activity. Moreover, the heterogenization allowed using the obtained organic-inorganic hybrids in water and thus, to increase the overall sustainability of the catalytic C-H arylation reaction. In addition, the solids were employed in multiple cycles showing good and stable catalytic activity.

Finally, we attempted to use the obtained materials in one of the most challenging and important transformations of our time: photocatalytic CO2 reduction. A set-up of the experiment and the quantification methods were performed. Some experiments involving the use of our heterogeneous PC were carried out, using different experimental conditions. As a result, important insights on the mechanism of this arduous transformation were highlighted.
Date of Award31 Jan 2022
Original languageEnglish
Awarding Institution
  • University of Namur
SponsorsFEDER Région Wallonne
SupervisorCarmela APRILE (Supervisor), Davide BONIFAZI (Co-Supervisor), Stephane Vincent (President), Steve Lanners (Jury), Paolo Pescarmona (Jury) & Roberto Lazzaroni (Jury)

Keywords

  • organic semiconductors
  • photocatalysis
  • heterogeneous catalysis
  • C-H arylation
  • CO2 photoreduction

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