Plastic mulch films are widely used in agriculture to conserve water, regulate soil temperature, and improve crop production. Yet after repeated exposure to sunlight, weathering, and mechanical stress, these films can fragment into polyethylene microplastics, which persist in soils and surrounding waters for decades or even centuries.
Now, researchers have developed a waste-to-resource strategy that uses agricultural biomass to help address this growing pollution problem. In a study published in Biochar, the team engineered a core-shell titanium dioxide and biochar composite capable of accelerating the photodegradation of polyethylene microplastics under light irradiation.
The most effective material, named 12TJBC, was made by combining core-shell TiO₂ with walnut shell-derived biochar. In laboratory tests, it reduced polyethylene microplastic particles from about 500 micrometers to less than 70 micrometers within 40 hours, performing 2.8 times better than pristine TiO₂.
"Plastic mulch is important for modern agriculture, but its long-term residues are becoming a serious environmental challenge," said corresponding author Professor Jiehong He. "Our goal was to design a sustainable material that not only uses agricultural waste as a resource, but also improves the breakdown of persistent polyethylene microplastics."
TiO₂ is already known as a promising photocatalyst, meaning it can use light energy to trigger chemical reactions. However, its performance is often limited by rapid recombination of photogenerated charges and poor use of visible light. The new study shows that biochar can help overcome these limitations.
According to the researchers, walnut shell biochar plays several roles at once. It provides a porous surface that helps capture microplastic particles, forms Ti–O–C interfacial bonds with TiO₂ to improve charge transfer, and narrows the TiO₂ bandgap from 3.19 to 2.74 eV, allowing the composite to harvest light more effectively. These changes promote the generation of reactive oxygen species, especially hydroxyl radicals, which were identified as the dominant drivers of microplastic oxidation.
The team also examined a less studied factor: dissolved organic matter released from biochar during photocatalysis. Such dissolved organic matter is often viewed as a possible obstacle because it can block light. Surprisingly, the walnut shell biochar-derived dissolved organic matter acted instead as a co-catalyst, enhancing electron-accepting capacity and promoting radical generation without causing notable light-shielding effects.
Further chemical analysis showed that the polyethylene microplastics followed a stepwise oxidation pathway. Long-chain hydrocarbon structures were first attacked through hydrogen abstraction and chain scission, then converted into oxygen-containing intermediates and smaller products. Toxicity modeling using ECOSAR suggested that most intermediates had low ecological risk. Additional mung bean germination tests showed that solutions collected after different reaction times caused little inhibition, with germination rates remaining above 95%.
"This work helps clarify how biochar and TiO₂ cooperate at the interface, and how biochar-derived dissolved organic matter can actively participate in microplastic degradation," said Professor He. "These findings provide mechanistic guidance for designing safer and more efficient photocatalysts for agricultural plastic pollution control."
The researchers emphasize that the work is still at the laboratory stage, but it offers a promising direction for managing plastic residues in agricultural environments. By converting walnut shells into a functional component of photocatalysts, the study links biomass valorization, microplastic remediation, and sustainable agriculture in one integrated approach.
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Journal Reference: Li, Z., Chen, S., Sun, Y. et al. Synergetic polyethylene microplastic photodegradation over core–shell TiO2/biochar: unraveling the dual roles of interfacial bonding and biochar-derived DOM. Biochar 8, 117 (2026).
https://doi.org/10.1007/s42773-026-00625-9
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
