Lawson, T.; Gentleman, A.; Lage, A.; Casadevall, C.; Xiao, J.; Petit, T.; Frosz, M.; Reisner, E.; Euser, T.: Low-volume reaction monitoring of carbon dot light absorbers in optofluidic microreactors. ACS Catalysis 13 (2023), p. 9090–9101
10.1021/acscatal.3c02212
Open Access Version
Abstract:
Opticalmonitoringand screeningof photocatalyticbatch reactionsusing cuvettesexsituis time-consuming,requiressubstantialamountsof samples,and does not allow the analysisof specieswith low extinctioncoefficients.Hollow-core photoniccrystalfibers (HC-PCFs)providean innovativeapproachforinsitureactiondetectionusing ultraviolet−visibleabsorptionspectroscopy,with thepotentialfor high-throughputautomationusing extremelylow samplevolumeswith high sensitivityfor monitoringof the analyte.HC-PCFsuse interferenceeffects to guide light at the center of a microfluidicchanneland use this to enhancedetectionsensitivity.They open the possibilityof comprehensivelystudyingphotocatalyststo extractstructure−activityrelationships,which is unfeasiblewithsimilarreactionvolume,time, and sensitivityin cuvettes.Here, we demonstratethe use of HC-PCFmicroreactorsfor the screeningof the electrontransferpropertiesof carbondots (CDs),a nanometer-sizedmaterialthat is emergingas a homogeneouslightabsorberin photocatalysis.The CD-drivenphotoreductionreactionof viologens(XV2+) to the correspondingradicalmonocationXV•+is monitoredin situas a model reaction,using a samplevolumeof 1μL per measurementand with a detectabilityof <1μM. Arange of differentreactionconditionshave been systematicallystudied,includingdifferenttypes of CDs (i.e., amorphous,graphitic,and graphiticnitrogen-dopedCDs), surfacechemistry,viologens,and electrondonors.Furthermore,the excitationirradiancewasvaried to study its effect on the photoreductionrate. The findingsare correlatedwith the electrontransferpropertiesof CDs basedon their electronicstructurecharacterizedby soft X-ray absorptionspectroscopy.Optofluidicmicroreactorswith real-timeopticaldetectionprovideuniqueinsightinto the reactiondynamicsof photocatalyticsystemsand could form the basis of future automatedcatalystscreeningplatforms,where samplesare only availableon small scales or at a high cost.