Solar-driven H2O2 generation and photo-Fenton-like degradation of carbamazepine using P/In-modified g-C3N4: transformation products and ecotoxicity assessment

Solar-driven in situ hydrogen peroxide generation by semiconductor photocatalysts offers a promising strategy for integrating photocatalysis with Fe-assisted oxidation processes, enabling contaminant removal without the external addition of oxidants. In this work, a phosphorus- and indium-modified graphitic carbon nitride (P/In-C3N4) photocatalyst was investigated for H2O2 production and pollutant degradation, using carbamazepine (CBZ) as model contaminant. Under simulated solar irradiation (λ > 340 nm), P/In-C3N4 efficiently generated H2O2 via oxygen reduction, further enhanced in the presence of CBZ, suggesting that the pollutant acts as a hole scavenger, thereby improving charge separation and promoting the oxygen reduction pathway. Scavenger experiments indicated that photogenerated holes are the predominant reactive species involved in CBZ degradation, while hydroxyl radicals and superoxide radicals provide a secondary contribution. To improve degradation efficiency, the photocatalytic system was coupled with Fe-mediated Fenton-like and photo-Fenton-like reactions by exploiting the in situ generated H2O2, thus avoiding the external addition of oxidants. The combined process accelerated CBZ degradation with respect to photocatalysis alone and maintained high performance in real water matrices despite the presence of inorganic and organic matter. Transformation products were identified by LC–MS/MS, allowing the proposal of degradation pathways under both photocatalytic and photo-Fenton-like conditions. In silico ecotoxicity assessment (ECOSAR) indicated that several intermediates may exhibit higher toxicity than the parent compound, particularly toward green algae. Notably, the addition of Fe(III) greatly reduced the persistence of these hazardous transformation products, thereby lowering the overall ecotoxicological concern. These results highlight the potential of integrated photocatalytic/photo-Fenton systems for water treatment applications.