Enhanced Ibuprofen Degradation via BiOBr-Based Sonophotocatalysis: Synergy, Pathways and Reactor Insights

The need for advanced and energy-efficient water treatment technologies is driving renewed interest in advanced oxidation processes (AOPs), particularly photocatalysis, for the removal of persistent pharmaceutical contaminants [1]. However, conventional photocatalytic systems remain constrained by limited photon utilization, rapid electron–hole recombination, and gradual catalyst deactivation [1]. Ultrasound irradiation introduces unique cavitation-driven physical and chemical effects capable of overcoming many of these bottlenecks [2]. When combined with photocatalysis, these effects can significantly intensify mass transfer, radical formation, and surface regeneration, enabling synergistic oxidation pathways that are not accessible under either technique alone [2]. In this study, ultrasound-assisted oxidation processes were investigated for ibuprofen (IBU) degradation in aqueous media using a broadband multi-frequency ultrasonic reactor (584–1148 kHz). Experiments were performed on a 50 mg·L-1 IBU solution under three operating modes: sonocatalysis (US), photocatalysis (solar light, 35 W·m-2), and combined sonophotocatalysis (US and light) using bismuth oxybromide (BiOBr, 0.25 g·L-1) as a visible-light-responsive photocatalyst [2]. The integrated process significantly enhanced IBU removal compared to sonocatalysis and photocatalysis alone, due to improved reactive oxygen species (ROS) generation, mass transfer, charge carrier lifetime, and catalyst surface renewal. A synergy of 53% was observed, highlighting the importance of frequency distribution and reactor geometry. UHPLC–MS/MS analyses revealed distinct transformation product (TP) profiles for each mode. Photocatalysis produced a limited set of intermediates, sonocatalysis generated additional radical-driven TPs, and sonophotocatalysis exhibited a unique combination of degradation pathways, resulting in both accelerated removal and a broader spectrum of TPs. Comparative analysis of TPs allowed identification of major and minor reaction routes, demonstrating how ultrasound modulates oxidative pathways and reaction mechanisms. These insights are crucial for predicting product formation and designing safe, efficient water treatment processes. While the focus remains scientific, preliminary evaluation, including energy efficiency indicators and basic cost-of-ownership considerations, suggests that broadband multi-frequency reactors are compatible with scalable, energy-efficient operation, supporting their potential for practical application. In conclusion, this study demonstrates that synergistic sonophotocatalysis not only enhances ibuprofen degradation, but also directs transformation pathways, underscoring the value of coupling advanced reactor engineering with material performance for eco-efficient, mechanistically-informed AOPs. References [1] Galloni, M.G. et al., Curr. Opin. Chem. Eng., 48, 101129 (2025). [2] Falletta, E. et al., ACS Photonics, 10, 3929–3943 (2023).