Interfacial antagonism between goethite and ZnO nanoparticles modulates organic phosphorus fate in aquatic systems

Abstract

Iron (hydr)oxides and phosphorus interactions critically influence aquatic biogeochemical cycles, yet the role of engineered nanoparticles in modulating these processes remains underexplored. This study systematically investigates how zinc oxide nanoparticles (ZnO NPs) and goethite (Gt) synergistically regulate the transformation of five representative organic phosphorus (OP) compounds—inositol hexaphosphate, nucleic acids, 2-aminoethylphosphonic acid, adenosine triphosphate, and creatine phosphate. Gt alone exhibited limited OP degradation (14.7 %–39.2 % over 80 h). In contrast, co-treatment with ZnO NPs enhanced degradation efficiencies to 20.3 %–46.4 %, while sequential addition of ZnO NPs prior to Gt further increased mineralization to 37.1 %–75.6 %, highlighting the importance of treatment sequence. Mechanistically, photogenerated hydroxyl (·OH) and superoxide (·O₂^¯) radicals drove OP transformation in ZnO NP systems. Surface and molecular characterizations (XPS, AFM, synchrotron-based XANES) confirmed that OPs formed bidentate inner-sphere complexes with Gt, which limited photoreactivity by attenuating light penetration. Sequential addition of ZnO NPs or Zn²⁺ substitution circumvented Gt–OP–Zn complex formation, significantly improving OP mineralization. Adsorption kinetics and isotherm modeling revealed Gt’s dominant role in OP sequestration via inner-sphere complexation, which inhibited radical access to surface-bound species. These findings underscore the antagonistic yet tunable interplay between Fe oxides and photocatalytic nanoparticles in regulating phosphorus fate, offering valuable mechanistic insights for the design of nanomaterial-enhanced strategies to mitigate OP-driven eutrophication in aquatic environments.