Beyond mass transfer: Bubble-propelled Fenton catalysts for efficient benzohydroxamic acid degradation

The increasing discharge of mineral processing wastewater containing recalcitrant benzohydroxamic acid (BHA) poses significant environmental and health risks. This work developed a Pt@HNT/Fe₃O₄ (PHF) bubble-propelled catalyst by encapsulating Pt nanoparticles within halloysite nanotubes (HNT) lumens and anchoring Fe₃O₄ on the exterior surface to degrade BHA. The PHF/H₂O₂ system achieved 90% BHA degradation efficiency within 90 min, significantly outperforming conventional HNT/Fe₃O₄ (HF)/H₂O₂ system (38%). Mechanistic studies integrating density functional theory (DFT) calculations and experimental results revealed that bubble enhances reactive oxygen species (ROS) exposure while unchanged the dominant species. Beyond widely reported mass transfer enhancement, bubbles amplify interfacial heterogenous Fenton reactivity by enhancing ROS generation, lowering activation energy barriers for H₂O₂ dissociation, and stabilizing hydroxyl radical (·OH) accumulation at gas-liquid interfaces. The degradation of BHA was dominated ·OH, which preferentially attacked the amide group of BHA via hydrogen atom transfer (HAT). This work redefines bubbles as multifunctional interfacial modulators rather than conventional mixing enhancers, offering new insights into bubble-propelled catalytic systems and establishing theoretical frameworks for understanding BHA degradation pathways and environmental fate.