Abstract
Mechanistically derived predictive kinetic models for photocatalytic processes have inherent challenges due to short lived charge carriers and free radical intermediate species. In this work, we present a spectro-kinetic model for the photocatalytic oxidation of carbazole (CAB), a nitrogen-containing heterocyclic compound, using a visible-light-active Ag/AgBr/TiO(2) photocatalyst immobilized on glass beads. Experiments were performed in a continuous-flow packed bed photoreactor in industrial wastewater matrix under visible light. Reactive oxygen species (ROS) were monitored using electron paramagnetic resonance (EPR) spectroscopy, identifying hydroxyl radicals (˙OH) as the predominant ROS, with superoxide (O(2)˙(-)). and H(2)O(2) acting as intermediates. The model incorporates key pathways including direct hole oxidation and ˙OH-mediated oxidation of CAB, as well as charge recombination and radical quenching. Quenching of (˙OH) by intermediate CAB-derived ˙CR radicals emerged as the rate-determining step, exerting the greatest impact on apparent quantum efficiency (AQE). The model showed excellent agreement with experimental results (R (2) = 0.99), accurately predicting CAB degradation kinetics. Parametric analysis confirmed ˙OH radical mediated oxidation as the primary pathway, followed by secondary contribution from direct h(+) attack. The system achieved 54% CAB removal with an AQE of 75%. This study demonstrates the value of integrating spectroscopic measurements with mechanistic modeling to guide photocatalytic process development.