A new study demonstrates that agricultural waste can be transformed into a powerful, eco-friendly catalyst that dramatically improves the removal of stubborn chemical pollutants from water. Researchers developed a nitrogen-doped biochar made from cotton hulls that enhances ozone-based water treatment efficiency by more than 100 times, offering a promising solution for tackling emerging contaminants.
The study, published in Biochar, focuses on removing N,N-diethyl-meta-toluamide (DEET), a widely used insect repellent frequently detected in rivers, lakes, and wastewater. Because DEET is resistant to conventional treatment methods, it has become a representative micropollutant of growing environmental concern.
"By converting agricultural waste into a high-performance catalyst, we created a sustainable material that can significantly accelerate pollutant degradation in water," said one of the study's authors. "This approach not only improves treatment efficiency but also adds value to biomass resources that would otherwise be discarded."
The research team synthesized a nitrogen-doped biochar, referred to as N-BC-800, using cotton hulls and urea through a controlled high-temperature process. The resulting material contains abundant active sites, including pyridinic nitrogen and carbonyl groups, which play a critical role in catalysis.
When applied to ozone-based water treatment, the catalyst showed remarkable performance. The apparent reaction rate for DEET degradation increased by more than 100-fold compared to ozone alone. In laboratory tests, the system achieved up to 94 percent removal efficiency, far surpassing untreated biochar or conventional ozonation processes.
The key to this improvement lies in how the catalyst interacts with ozone. Instead of relying on ozone molecules alone, the biochar promotes the formation of highly reactive oxygen species such as hydroxyl radicals and superoxide radicals. These species are far more effective at breaking down complex organic pollutants into simpler, less harmful compounds.
"Our findings show that the catalyst converts ozone into more reactive forms that can rapidly attack contaminants," the author explained. "This significantly reduces treatment time and improves overall efficiency."
Beyond DEET, the catalyst also demonstrated strong performance against a range of common pollutants, including pharmaceuticals and herbicides. This broad-spectrum capability suggests that the material could be applied in diverse water treatment scenarios.
Importantly, the catalyst maintained high performance under realistic environmental conditions. Tests showed that natural organic matter and common ions in water had minimal impact on degradation efficiency. The material also retained about 80 percent of its activity after multiple reuse cycles, indicating strong stability and durability.
Another critical advantage is safety. Toxicity assessments revealed that the treatment process not only removes pollutants but also reduces the toxicity of byproducts. Experiments using luminescent bacteria confirmed that treated water exhibited significantly lower biological toxicity compared to ozone treatment alone.
"This means the process is not just effective, but also safer for ecosystems and potentially for human health," the researchers noted.
The study highlights a broader opportunity to integrate waste valorization with environmental remediation. By turning agricultural residues into advanced functional materials, the approach supports circular economy principles while addressing urgent water quality challenges.
With increasing concern over emerging contaminants in water supplies worldwide, the development of efficient, low-cost, and sustainable treatment technologies is becoming essential. This nitrogen-doped biochar catalyst represents a promising step toward scalable solutions for cleaner and safer water systems.
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Journal Reference: Wang, C., Gao, Y., Guo, Z. et al. Synergistic catalytic ozonation by pyridinic N and C=O groups on cotton hulls biochar for efficient DEET degradation. Biochar 8, 84 (2026).
https://doi.org/10.1007/s42773-026-00607-x
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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.
