Evaluation of photon fluxes, external mass transfer and heterogeneous quantum yield in an Optofluidic threaded microreactor (OTM)

Abstract

This study presents a comprehensive methodology to evaluate photon fluxes, external mass transfer, and heterogeneous quantum yield within a microchannel-type optofluidic microrreactor. It has been specifically applied to an optofluidic threaded microreactor (OTM), tested in the photodegradation of aqueous ibuprofen acid under UVA irradiation. The given approach facilitates the calculation of heterogeneous quantum yields, avoiding the need for specialized radiometers and relying instead on the spectral characterization of the reactor components. By employing flow-mode ferrioxalate actinometry, the photon flux within the OTM was accurately determined, simultaneously allowing evaluation of the average optical path length. The results highlight the high radiation utilization ratio in the OTM. The optical properties of the catalytic layer, composed of TiO₂ nanoparticles and a primer, were characterized through the Kubelka-Munk theory and the Bouguer-Beer law, which allowed the estimation of the active shell thickness. The reaction rate equation, which included the effect of external mass transfer resistance through a modified Sherwood number correlation, could be analytically integrated to evaluate residence time, thus allowing the estimation of reaction orders and kinetic and equilibrium constants by error minimization. The OTM shows a relative photonic efficiency of 1.6 for the photodegradation of ibuprofen. This work provides a robust method for evaluating photocatalytic performance in microchannel-type reactors, offering insights into the effect of geometric and operational parameters on photon absorption, mass transfer, and quantum yield.