Synergetic polyethylene microplastic photodegradation over core–shell TiO₂/biochar: unraveling the dual roles of interfacial bonding and biochar-derived DOM

Abstract

The pervasive accumulation of polyethylene (PE) microplastics (MPs) from agricultural mulch films represents a critical threat to soil health and ecological stability. In this study, we developed a sustainable “waste-to-resource” strategy by engineering biomass-derived biochar/core–shell TiO₂ (BC/CST) composites for the efficient remediation of PE-MPs. Walnut shell biochar-optimized core–shell structural TiO₂ composites (12TJBC) achieved superior performance, reducing PE-MPs size from 500 μm to <70 μm within 40 h, outpacing pristine TiO₂ by 2.8-fold. Systematic characterization revealed that the superior activity originates from the synergistic effects of Ti–O–C interfacial bonding and bandgap narrowing (from 3.19 to 2.74 eV), which facilitates efficient charge separation and visible-light harvesting. Mechanistic investigations identified hydroxyl radicals (•OH) as the dominant reactive oxygen species (ROS), with steady-state concentrations reaching 8.84 μM. A unique focus was placed on the environmental chemistry of biochar-derived dissolved organic matter (JDOM). We found that JDOM acts as a co-catalyst to amplify degradation by enhancing electron-accepting capacity, effectively counteracting its inherent light-shielding effects. Furthermore, the chemical fate of PE-MPs was elucidated through two-dimensional correlation spectroscopy (2D-COS) and GC–MS, revealing a sequential oxidation pathway from long-chain alkanes to low-toxicity oxygenated intermediates. Ecotoxicological assessments via ECOSAR confirmed the environmental safety of the products. This work provides a dual-phase synergistic framework for mitigating plastic pollution while ensuring ecotoxicological integrity in agricultural ecosystems.

Graphical Abstract

Keywords

Polyethylene microplastics / Photocatalysis / Biochar / TiO₂ / DOM

Highlight

•	Various core–shell TiO2/biochar composites were successfully prepared.
•	Walnut shell biochar enhanced interfacial charge transfer via Ti–O-C bonds.
•	Hydroxyl radicals dominated the photocatalytic PE microplastics degradation.
•	Biochar-derived DOM amplified ROS generation without light-shielding effects.
•	A stepwise degradation pathway of PE microplastics was resolved via 2D-COS and GC–MS.

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Funding

National Natural Science Foundation of China(52300197)

Aeronautical Science Foundation of China(42577474)

RIGHTS & PERMISSIONS

The Author(s)