Optical monitoring and screening of photocatalytic batch
reactions
using cuvettesex situis time-consuming, requires
substantial amounts of samples, and does not allow the analysis of
species with low extinction coefficients. Hollow-core photonic crystal
fibers (HC-PCFs) provide an innovative approach forin situreaction detection using ultraviolet–visible absorption spectroscopy,
with the potential for high-throughput automation using extremely
low sample volumes with high sensitivity for monitoring of the analyte.
HC-PCFs use interference effects to guide light at the center of a
microfluidic channel and use this to enhance detection sensitivity.
They open the possibility of comprehensively studying photocatalysts
to extract structure–activity relationships, which is unfeasible
with similar reaction volume, time, and sensitivity in cuvettes. Here,
we demonstrate the use of HC-PCF microreactors for the screening of
the electron transfer properties of carbon dots (CDs), a nanometer-sized
material that is emerging as a homogeneous light absorber in photocatalysis.
The CD-driven photoreduction reaction of viologens (XV2+) to the corresponding radical monocation XV•+is
monitoredin situas a model reaction, using a sample
volume of 1 μL per measurement and with a detectability of <1
μM. A range of different reaction conditions have been systematically
studied, including different types of CDs (i.e.,
amorphous, graphitic, and graphitic nitrogen-doped CDs), surface chemistry,
viologens, and electron donors. Furthermore, the excitation irradiance
was varied to study its effect on the photoreduction rate. The findings
are correlated with the electron transfer properties of CDs based
on their electronic structure characterized by soft X-ray absorption
spectroscopy. Optofluidic microreactors with real-time optical detection
provide unique insight into the reaction dynamics of photocatalytic
systems and could form the basis of future automated catalyst screening
platforms, where samples are only available on small scales or at
a high cost.