Mechanistic Divergence and Ozone Mass Transfer Enhancement in Photocatalytic Ozonation: A Comparative Study of Bimetallic Pd/Cu-Modified Rutile TiO2 and g-C3N4

Abstract Beyond conventional removal-efficiency metrics, this investigation reveals a mechanistic divergence between two prominent photocatalysts in ozone activation. Both (Pd/Cu) bimetallic g-C3N4 and rutile TiO2 enable efficient antibiotic degradation and antibiotic resistance genes inactivation; however, they rely on fundamentally different reaction pathways. (Pd/Cu)1%C3N4 predominantly generates reactive oxygen species (ROS), including singlet oxygen (1O2) and superoxide radical anion (O2●–), whereas (Pd/Cu)1%TiO2 targets specific sequences like intl1 bypassing conventional ROS pathways. In addition, our research highlights a critical design trade-off and operational paradox in advanced oxidation processes: while a low bimetallic loading (0.1 wt %) optimizes the initial chemical degradation kinetics of both antibiotics and antibiotic resistance genes during active treatment, a higher loading (1.0 wt %) is strictly indispensable for suppressing long-term bacterial regrowth and preventing the biological resuscitation of resistance markers during post-treatment storage. Moreover, this study challenges conventional methodological paradigms by demonstrating that diagnostic scavengers are not inert probes but reactive species that accelerate ozone (O3) depletion and alter mass-transfer behavior, potentially confounding mechanistic interpretations. In complex wastewater matrices dominated by dissolved organic matter, such competitive interactions necessitate rigorous scavenger validation to ensure reliable translation of laboratory findings to scalable purification systems.