Construction of Mn3O4@BiOBr direct Z-scheme heterojunction for efficient norfloxacin removal: Distinguishing adsorptive and photocatalytic pathways

Efficient charge transfer is crucial for photocatalytic pollutant removal, essential for sustainable water treatment. Herein, a Mn3O4@BiOBr heterojunction was synthesized via a simple hydrothermal method, combining the multivalent redox properties of Mn3O4 with the visible-light responsiveness of BiOBr. Under irradiation, the removal efficiency of norfloxacin (NOR) increased from approximately 80% with pristine BiOBr to around 90% with Mn3O4@BiOBr, attributed to the enhanced suppression of electron–hole recombination. Radical scavenging tests revealed that photogenerated holes (h+) and superoxide radicals (O2•−) were the primary reactive species driving the degradation process. The kinetics of NOR degradation were significantly influenced by competitive adsorption of co-existing anions and the complexation with divalent cations. Despite high stability, the reusability of the composite was limited by the accumulation of NOR and intermediates on active sites, highlighting the need to accelerate product desorption. This study provides mechanistic insights and practical guidance for designing visible-light-driven photocatalysts for efficient antibiotic removal.