Enzyme-driven biodegradation of Ti3C2 MXene: unveiling peroxidase-mediated pathways and enhanced bioaccumulation risks in aquatic systems

Abstract

2D MXene nanosheets are increasingly attracting interest due to their promising applications in materials science and biomedicine. However, the environmental fate of MXenes, particularly their biotransformation, is poorly understood. Here, the biodegradability of Ti₃C₂ MXene nanosheets was investigated using a plant horseradish peroxidase (HRP)-mediated reaction. The degradation rates of Ti₃C₂ MXene nanosheets were determined to be first-order in both HRP and H₂O₂ dosage. Material characterization and product identification revealed that peroxidasecatalyzed the oxidation of Ti₃C₂ MXene in the presence of H₂O₂, resulting in the formation of holes on its basal plane, the generation of titanium dioxide (TiO₂) nanoparticles, and the release of CO₂. The assessment using Daphnia magna revealed visible toxicity and enrichment of Ti₃C₂ MXene to aquatic organisms, with LC₅₀ values of pristine Ti₃C₂ MXene to Daphnia being 55.41, 7.24, and 2.97 mg L⁻¹ at 48, 72, and 96 h, respectively. Substantial accumulation (74.30 μg Ti per mg of dry tissue) of Ti₃C₂ MXene by Daphnia was observed after 48 h of exposure. Furthermore, the biological effects of HRP-degraded Ti₃C₂ MXene products on Daphnia were examined. Although the toxicity to Daphnia was reduced, a substantial increase in the bioaccumulation of Ti₃C₂ MXene biodegradation products (137.36 μg Ti per mg of dry tissue) was observed. These findings reveal that enzymatic degradation alters the size and surface chemistry of Ti₃C₂ MXene, potentially changing its toxicity and altering its environmental compatibility.