In-situ monitoring of photocatalytic reactions in optofluidic microreactors
To advance the state-of-the-art technology in photocatalysis, there is a growing need to develop optically efficient microreactors that allow rapid changes in reaction conditions for catalyst screening. In addition, such microreactors should offer strong light-matter interactions for the in-situ spectroscopic detection of chemical species. Motivated by these challenges, this thesis marries the fields of fibre-based optofluidics and photocatalysis to generate scientific insights into how promising new photocatalysts behave.
Novel types of optical fibre were optimised and characterised for liquid phase spectroscopy on sub-microlitre samples; these fibres included kagomé-style and single-ring hollow-core photonic crystal fibres (HC-PCFs). New kinetic insights were obtained into the photoactivity of carbon nanodots (CDs) through systematic screening of a wide range of reaction conditions within kagomé-style HC-PCF microreactors.
Spectrokinetic insights across twenty-nine reaction conditions were studied with a cumulative sample volume of < 1.5 mL, using viologen species as indicators of electron transfer from CDs. First, amorphous and graphitic CDs were benchmarked against the well-known photocatalyst [Ru(bpy)3]2+. This study was then extended to replace the viologen indicator with hydrogen-evolving cobaloxime electrocatalysts, to probe catalytic intermediate states.
To give further insight into the electron transfer from carbon nanodots to viologens, transient absorption spectroscopy was then performed to probe changes on timescales of 1 nanosecond to 1 millisecond.
Finally, a new ultralow volume fibre-based fluorescence spectroscopy method was realised. As a proof of principle, the photoredox catalyst 4CzIPN was combined with the fluorescence quenchers tetrabutylammonium azide and cyclohexylamine. The extracted bimolecular Stern-Volmer quenching coefficients were compared with conventional fluorimeter-based approaches, which were taken on much larger sample volumes.
This thesis provides a foundation for developing continuous-flow photocatalytic screening systems based on HC-PCFs, which minimise the consumption of precious reagents.
Engineering and Physical Sciences Research Council (1948662)