Effect of Hematite Morphology on the Photosensitive Response of Microplastic-Derived Dissolved Organic Matter
The interaction between microplastic-derived dissolved organic matter (PSDOM) and iron oxides in soil environments can modulate its photosensitization effects, yet the underlying mechanisms remain elusive. This study investigated the influence of hematite with distinct morphologies—flake-shaped (HNPs) and cubic (HNCs)—on the photosensitization of polystyrene-derived dissolved organic matter (PSDOM). Under 500 W mercury lamp irradiation, both hematite morphologies promoted PSDOM degradation, with HNCs exhibiting superior performance: total organic carbon (TOC) decreased from 18.4 mg·L−1 to 12.3 mg·L−1 within 90 min, compared to 13.3 mg·L−1 for HNPs. Three-dimensional fluorescence spectroscopy indicated that hematite alters the humification process, thereby modifying photosensitization. Electron paramagnetic resonance (EPR) spectroscopy identified the generation of singlet oxygen (1O2), hydroxyl radicals (·OH), and carbon-centered radicals (CH3C(=O)OO·). HNCs significantly enhanced 1O2 production, while HNPs favored ·OH generation; both inhibited CH3C(=O)OO· formation. Quantitative analysis via high-performance liquid chromatography revealed that the steady-state concentration of 1O2 was highest with HNCs, reaching 2.80 times that of the PSDOM control, whereas ·OH concentration peaked with HNPs at 1.98 times the control. Notably, the steady-state concentration of 1O2 was approximately three orders of magnitude higher than that of ·OH. These findings elucidate the morphology-dependent role of hematite in PSDOM photosensitization, providing mechanistic insights into the environmental fate of microplastic-derived organic matter in complex soil systems.